Adjustable collimators method and system

ABSTRACT

Embodiments relate to collimator assemblies having one or more apertures therein. At least one of the one or more apertures has an aperture size that is configured for adjustment during an examination. The collimator assembly is configured so that gamma rays can pass through the one or more apertures, but the remainder of the collimator assembly is substantially gamma ray absorbent. Embodiments also related to imaging systems and methods of imaging.

BACKGROUND

The invention relates generally to non-invasive imaging such as singlephoton emission computed tomography (SPECT) imaging. More particularly,the invention relates to adjustable collimators for use in non-invasiveimaging.

SPECT is used for a wide variety of imaging applications, such asmedical imaging. In general, SPECT systems are imaging systems that areconfigured to generate an image based upon the impact of photons(generated by a nuclear decay event) against a gamma-ray detector. Inmedical and research contexts, these detected photons may be processedto formulate an image of organs or tissues beneath the skin.

To produce an image, one or more detector assemblies may be rotatedaround a subject. Detector assemblies are typically comprised of variousstructures working together to receive and process the incoming photons.For instance, the detector assembly may utilize a scintillator assembly(e.g., large sodium iodide scintillator plates) to convert the photonsinto visible light for detection by an optical sensor. This scintillatorassembly may be coupled by a light guide to multiple photomultipliertubes (PMTs) or other light sensors that convert the light from thescintillator assembly into an electric signal. In addition to thescintillator assembly-PMT combination, pixilated solid-state directconversion detectors (e.g., CZT) may also be used to generate electricsignals from the impact of the photons. This electric signal can betransferred, converted, and processed by electronic modules in a dataacquisition module to facilitate viewing and manipulation by clinicians.

Typically, SPECT systems further include a collimator assembly that maybe attached to the front of the gamma-ray detector. In general, thecollimator assembly is designed to absorb photons such that only photonstraveling in certain directions impact the detector assembly. Thecollimator assembly selected for use with the SPECT system impacts thesystem performance thereof, including image resolution and sensitivity.Because resolution and sensitivity may be traded off along a collimatorperformance curve for each SPECT system, a single operating pointtypically may be selected when designing a collimator assembly. In otherwords, a collimator assembly is typically designed to operate at asingle operating point on the resolution-sensitivity tradeoffperformance curve. Different applications, however, may benefit fromoperating with different tradeoffs on the performance curve. By way ofexample, small organ imaging typically may require higher resolution andlower sensitivity, whereas imaging a large volume (such as for possiblelesions) typically may require higher sensitivity with lower resolution.

To provide a SPECT system with different tradeoffs on the performancecurve, multiple collimator assemblies may be provided for each SPECTsystem with each of the collimator assemblies having a differentperformance point. In this manner, a user may have a choice in selectinga collimator assembly with an appropriate operating point for aparticular application. Accordingly, when the user changes applications,the most appropriate collimator assembly must be mounted on the SPECTsystem. Collimator assemblies, however, are typically heavy, generallycomprising lead with a thickness sufficient to block gamma rays so thatthe collimator exchange is a time consuming process. To minimize thistime-consuming exchange, extra effort may be made to schedule blocks ofpatients with similar examination requirements, for example, in clinicallaboratories. In addition to the problems associate with thetime-consuming exchange of the collimator assemblies, the purchase andstorage of multiple collimator assemblies is costly.

Accordingly, it would be desirable to provide an imaging system withcollimator assemblies having different operating points along theresolution-sensitivity tradeoff performance curve while reducing theneed for multiple collimator assemblies.

BRIEF DESCRIPTION

In accordance with one embodiment, the present technique provides acollimator assembly. The collimator assembly includes one or moreapertures therein, wherein at least one of the one or more apertures hasan aperture size that is configured for adjustment during anexamination. The collimator assembly is configured so that gamma rayscan pass through the one or more apertures, but the remainder of thecollimator assembly is substantially gamma ray absorbent.

In accordance with another embodiment, the present technique provides animaging system including a collimator assembly and a detector assembly.The imaging system includes a collimator assembly having one or moreapertures therein wherein at least one of the one or more apertures hasan aperture size that is configured for adjustment during anexamination. The detector assembly is configured to generate one or moresignals in response to gamma rays that pass through the one or moreapertures in the collimator assembly.

In accordance with another embodiment, the present technique provides amethod of imaging a volume. The method includes positioning at least aportion of a subject in a field of view of an imaging system. Theimaging system includes a collimator assembly and a detector assembly.The method further includes adjusting an aperture size of at least oneaperture in the collimator assembly while the portion of the subject ispositioned in the field of view. The method further includes collimatinggamma rays emitted from the subject using the collimator assembly. Themethod further includes detecting the collimated gamma rays.

In accordance with another embodiment, the present technique provides amethod of imaging a volume. The method includes positioning at least aportion of a subject in a field of view of an imaging system. Theimaging system includes a collimator assembly and a detector assembly.The method further includes collimating gamma rays emitted from thesubject using the collimator assembly. The method further includesdetecting the collimated gamma rays. The method further includesadjusting an aperture size of at least one aperture in the collimatorassembly to increase resolution of the imaging system. The methodfurther includes collimating gamma rays emitted from the subject usingthe adjusted collimator assembly. The method further includes detectingthe collimated gamma rays.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is an illustration of an exemplary SPECT system which may includea collimator assembly in accordance with embodiments of the presenttechnique;

FIG. 2 is a perspective view of an exemplary SPECT system that includesa pinhole aperture collimator in accordance with embodiments of thepresent technique;

FIG. 3 is an exploded perspective view of an exemplary collimatorassembly having one or more adjustable pinhole apertures therein, thecollimator assembly including an inner pinhole aperture collimator andan outer pinhole aperture collimator in accordance with embodiments ofthe present technique;

FIGS. 4 and 5 are enlarged views of a portion of a collimator assemblysimilar to the collimator assembly in FIG. 3 to illustrate an adjustablepinhole aperture in accordance with embodiments of the presenttechnique;

FIG. 6 is a perspective, cut-away view of a collimator assembly similarto the collimator assembly of FIG. 3 to illustrate the adjustableapertures therein in accordance with embodiments of the presenttechnique;

FIGS. 7 and 8 are illustrations of an exemplary diaphragm that includesa plurality of blocks arranged to define an adjustable pinhole aperturein accordance with embodiments of the present technique.

FIG. 9 is a side view of the exemplary diaphragm of FIG. 7 to illustratethe edge configurations of the blocks in accordance with embodiments ofthe present technique;

FIG. 10 is a side view of an exemplary diaphragm having blocks withalternative edge configurations to the diaphragm of FIG. 9, inaccordance with embodiments of the present technique;

FIG. 11 is a perspective view of one block of the diaphragm of FIG. 7 inaccordance with embodiments of the present technique;

FIG. 12 is a top, perspective view of a diaphragm similar to thediaphragm of FIG. 7 and that includes a lever for adjusting the aperturesize in accordance with embodiments of the present technique;

FIG. 13 is another view of the exemplary diaphragm of FIG. 12, inaccordance with embodiments of the present technique;

FIG. 14 is a perspective view of another exemplary collimator assemblyhaving one or more adjustable pinhole apertures therein, each of thepinhole apertures defined by a diaphragm similar to the diaphragm ofFIG. 7 in accordance with embodiments of the present technique;

FIG. 15 is a perspective view of an exemplary SPECT system that includesa slit aperture collimator in accordance with embodiments of the presenttechnique;

FIG. 16 is an exploded perspective view of exemplary collimator assemblyhaving one or more adjustable slit apertures therein, the collimatorassembly including an inner and outer collimator in accordance withembodiments of the present technique;

FIG. 17 is a perspective view of a portion of the exemplary collimatorassembly of FIG. 16 in accordance with embodiments of the presenttechnique;

FIG. 18 is an enlarged view of a portion of the exemplary collimatorassembly of FIG. 17 taken along line 17 in accordance with embodimentsof the present technique;

FIGS. 19 and 20 are illustrations of another exemplary collimatorassembly having a plurality of adjustable slit apertures therein inaccordance with embodiments of the present technique;

FIG. 21 is an illustration of two panels of a slit aperture collimatorthat define an adjustable slit aperture in accordance with embodimentsof the present technique;

FIGS. 22 and 23 are side views of an adjustable slit aperture similar tothe adjustable slit aperture of FIG. 21 in accordance with embodimentsof the present technique;

FIG. 24 is a perspective view of another exemplary collimator assemblyhaving one or more adjustable slit apertures therein, the collimatorassembly including a first set of panels and a second set of panels inaccordance with embodiments of the present technique;

FIG. 25 is a perspective view of the collimator assembly of FIG. 24 toillustrate adjustment of slit aperture size in accordance withembodiments of the present technique;

FIG. 26 is an end view of the collimator assembly of FIG. 24 inaccordance with embodiments of the present technique;

FIG. 27 is a perspective view of a collimator assembly similar to thecollimator assembly of FIG. 24 and having side rods for positioning thefirst and second set of panels in accordance with embodiments of thepresent technique;

FIG. 28 is an illustration of one panel similar to the panels of theexemplary collimator assembly of FIG. 24 in accordance with embodimentsof the present technique;

FIG. 29 is a perspective view an exemplary collimator assembly having aslit aperture portion and a pinhole aperture portion in accordance withembodiments of the present technique;

FIG. 30 is an exploded perspective view of an exemplary collimatorassembly that includes an inner slit collimator and an outer slitcollimator in accordance with embodiments of the present technique;

FIG. 31 is an illustration of a portion of a detector assembly and aportion of the collimator assembly of FIG. 30 in accordance withembodiments of the present technique;

FIG. 32 is an illustration of an exemplary combined SPECT and computedtomography (CT) system in accordance with embodiments of the presenttechnique; and

FIG. 33 is an illustration of an exemplary CT system that can becombined with a SPECT system, in accordance with embodiments of thepresent technique.

DETAILED DESCRIPTION I. Exemplary SPECT System

FIG. 1 illustrates an exemplary SPECT system 10 for acquiring andprocessing image data in accordance with exemplary embodiments of thepresent technique. In the illustrated embodiment, SPECT system 10includes a collimator assembly 12 and a detector assembly 14. The SPECTsystem 10 also includes a control module 16, an image reconstruction andprocessing module 18, an operator workstation 20, and an image displayworkstation 22. Each of the aforementioned components will be discussedin greater detail in the sections that follow.

As illustrated, a subject support 24 (e.g. a table) may be moved intoposition in a field of view 26 of the SPECT system 10. In theillustrated embodiment, the subject support 24 is configured to supporta subject 28 (e.g., a human patient, a small animal, a plant, a porousobject, etc.) in a position for scanning. Alternatively, the subjectsupport 24 may be stationary, while the SPECT system 10 may be movedinto position around the subject 28 for scanning. Those of ordinaryskill in the art will appreciate that the subject 28 may be supported inany suitable position for scanning. By way of example, the subject 28may be supported in the field of view 26 in a generally verticalposition, a generally horizontal position, or any other suitableposition (e.g., inclined) for the desired scan. In SPECT imaging, thesubject 28 is typically injected with a solution that contains aradioactive tracer. The solution is distributed and absorbed throughoutthe subject 28 in different degrees, depending on the tracer employedand, in the case of living subjects, the functioning of the organs andtissues. The radioactive tracer emits electromagnetic rays 30 (e.g.,photons or gamma quanta) known as “gamma rays” during a nuclear decayevent.

As previously mentioned, the SPECT system 10 includes the collimatorassembly 12 that receives the gamma rays 30 emanating from the subject28 positioned in the field of view 26. As will be described below, thecollimator assembly 12 is generally configured to limit and define thedirection and angular divergence of the gamma rays 30. In general, thecollimator assembly 12 is disposed between the detector assembly 14 andthe field of view 26. As will be discussed in more detail with respectto the following figures, the collimator assembly 12 may include one ormore of a slit aperture collimator, a pinhole aperture collimator, or acombination thereof. Accordingly, the collimator assembly generallycontains slit apertures, pinholes apertures, or both therethrough. Inaccordance with exemplary embodiments of the present technique, one ormore of the pinhole apertures and the slits apertures have an aperturesize that is adjustable. Those of ordinary skill in the art willappreciate that through adjustment of the aperture size the performanceof the collimator assembly 12 may be changed and thus the resolution andsensitivity of the SPECT system 10 may also be changed. Moreover, thecollimator assembly 12 may contain a radiation-absorbent material, suchas lead or tungsten, for example. Referring again to FIG. 1, thecollimator assembly 12 extends at least partially around the field ofview 26. In exemplary embodiments, the collimator assembly 12 may extendup to about 360° around the field of view 26. By way of example, thecollimator assembly 12 may extend from about 180° to about 360° aroundthe field of view 26.

The gamma rays 30 that pass through the collimator assembly 12 impactthe detector assembly 14. Due to the collimation of the gamma rays 30 bythe collimator assembly 12, the detection of the gamma rays 30 may beused to determine the line of response along which each of the gammarays 30 traveled before impacting the detector assembly 14, allowinglocalization of each gamma ray's origin to that line. In general, thedetector assembly 14 may includes a plurality of detector elementsconfigured to detect the gamma rays 30 emanating from the subject 28 inthe field of view 26 and passing through one or more apertures definedby the collimator assembly 12. In exemplary embodiments, each of theplurality of detector elements in the detector assembly 14 produces anelectrical signal in response to the impact of the gamma rays 30.

As will be appreciated by those of ordinary skill in the art, thedetector elements of the detector assembly 14 may include any of avariety of suitable materials and/or circuits for detecting the impactof the gamma rays 30. By way of example, the detector elements mayinclude a plurality of solid-state detector elements, which may beprovided as one-dimensional or two-dimensional arrays. In anotherembodiment, the detector elements of the detector assembly 14 mayinclude a scintillation assembly and PMTs or other light sensors.

Moreover, the detector elements may be arranged in the detector assembly14 in any suitable manner. By way of example, the detector assembly 14may extend at least partially around the field of view 26. In certainembodiments, the detector assembly 14 may include modular detectorelements arranged around the field of view 26. Alternatively, thedetector assembly 14 may be arranged in a ring that may extend up toabout 360° around the field of view 26. In certain exemplaryembodiments, the detector assembly 14 may extend from about 180° toabout 360° around the field of view 26. The ring of detector elementsmay include flat panels or curved detector surfaces (e.g., a NaIannulus). In one exemplary embodiment, the ring may comprise in therange from 9-10 solid-state detector panels with each detector panelcomprising four detector modules. Those of ordinary skill in the artwill appreciate that the ring need not be circular, for example, thedetector elements may be arranged in an elliptical ring or be contouredto the body profile of the subject 28. In addition, in certain exemplaryembodiments, the detector assembly 14 may be gimbaled on its supportbase, e.g., so that arbitrary slice angles may be acquired.

To acquire multiple lines of response emanating from the subject 28 inthe field of view 26 during a scan, the collimator assembly 12 may beconfigured to rotate about the subject 28 positioned within the field ofview 26. In accordance with exemplary embodiments, the collimatorassembly 12 may be configured to rotate with respect to the detectorassembly 14. By way of example, the detector assembly 14 may bestationary while the collimator assembly 12 may be configured to rotateabout the field of view 26. Alternatively, the detector assembly 14 mayrotate while the collimator assembly 12 is stationary. In certainexemplary embodiments, the collimator assembly 12 and the detectorassembly 14 may both be configured to rotate, either together orindependent of one another. Alternatively, if sufficient pinholeapertures and/or slit apertures are provided through the collimatorassembly 12, then no rotation may be required. Also, if the slitapertures are orthogonal to the longitudinal axis of the collimatorassembly 12 then no rotation may be required. Such exemplary embodimentcould include axial displacement of the collimator assembly 12 relativeto the detector assembly 14. By way of example, the detector assembly 14may be stationary while the collimator assembly 12 may be configured toslide along its axial direction. Alternatively, the detector assembly 14may slide along its axial direction while the collimator assembly 12 isstationary, for example. In certain exemplary embodiments, thecollimator assembly 12 and the detector assembly 14 may both beconfigured to slide, either together or independent of one another.

SPECT system 10 further includes a control module 16. In the illustratedembodiment, the control module 16 includes a motor controller 32 and adata acquisition module 34. In general, the motor controller 32 maycontrol the rotational and/or longitudinal speed and position of thecollimator assembly 12, the detector assembly 14, and/or the position ofthe subject support 24. The data acquisition module 34 may be configuredto obtain the signals generated in response to the impact of the gammarays 30 with the detector assembly 14. For example, the data acquisitionmodule 34 may receive sampled electrical signals from the detectorassembly 14 and convert the data to digital signals for subsequentprocessing by the image reconstruction and processing module 18.

Those of ordinary skill in the art will appreciate that any suitabletechnique for data acquisition may be used with the SPECT system 10. Byway of example, the data needed for image reconstruction may be acquiredin a list or a frame mode.

In one exemplary embodiment of the present technique, gamma ray events(e.g., the impact of gamma rays 30 on the detector assembly 14), gantrymotion (e.g., collimator assembly 12 motion and subject support 24position), and physiological signals (e.g., heart beat and respiration)may be acquired in a list mode. For example, a time-stamp may beassociated with each gamma ray event (e.g., energy and position) or byinterspersing regular time stamps (e.g., every 1 ms) into the list ofgamma ray events. The physiological signals may be included in the list,for example, when they change by a defined amount or with every regulartime stamp. In addition, gantry motion may also be included in the eventlists, for example, when it changes by a defined amount or with everyregular time stamp. The list mode data may be binned by time, gantrymotion or physiological gates before reconstruction. List mode may besuitable in exemplary embodiments where the count rate is relatively lowand many pixels record no counts at each gantry position orphysiological gate.

Alternatively, frames and physiological gates may be acquired by movingthe gantry in a step-and-shoot manner and storing the number of eventsin each pixel during each frame time and heart or respiration cyclephase. Frame mode may be suitable, for example, where the count rate isrelatively high and most pixels are recording counts at each gantryposition or physiological gate.

In the illustrated embodiment, the image reconstruction and processingmodule 18 is coupled to the data acquisition module 34. The signalsacquired by the data acquisition module 34 are provided to the imagereconstruction and processing module 18 for image reconstruction. Theimage reconstruction and processing module 18 may include electroniccircuitry to receive acquired signals and electronic circuitry tocondition the acquired signals. Further, the image reconstruction andprocessing module 18 may include processing to coordinate functions ofthe SPECT system 10 and implement reconstruction algorithms suitable forreconstruction of the acquired signals. The image reconstruction andprocessing module 18 may include a digital signal processor, memory, acentral processing unit (CPU) or the like, for processing the acquiredsignals. As will be appreciated, the processing may include the use ofone or more computers. The addition of a separate CPU may provideadditional functions for image reconstruction, including, but notlimited to, signal processing of data received, and transmission of datato the operator workstation 20 and image display workstation 22. In oneembodiment, the CPU may be confined within the image reconstruction andprocessing module 34, while in another embodiment a CPU may include astand-alone device that is separate from the image reconstruction andprocessing module 34.

The reconstructed image may be provided to the operator workstation 20.The operator workstation 20 may be utilized by a system operator toprovide control instructions to some or all of the described componentsand for configuring the various operating parameters that aid in dataacquisition and image generation: An image display workstation 22coupled to the operator workstation 20 may be utilized to observe thereconstructed image. It should be further noted that the operatorworkstation 20 and the image display workstation 22 may be coupled toother output devices, which may include printers and standard or specialpurpose computer monitors. In general, displays, printers, workstations,and similar devices supplied with the SPECT system 10 may be local tothe data acquisition components, or may be remote from these components,such as elsewhere within the institution or hospital, or in an entirelydifferent location, linked to the image acquisition system via one ormore configurable networks, such as the Internet, virtual privatenetworks, and so forth. By way of example, the operator workstation 20and/or the image reconstruction and processing module 18 may be coupledto a remote image display workstation 36 via a network (represented onFIG. 1 as Internet 38).

Furthermore, those of ordinary skill in the art will appreciate that anysuitable technique for image reconstruction may be used with the SPECTsystem 10. In one exemplary embodiment, iterative reconstruction (e.g.,ordered subsets expectation maximization, OSEM) may be used. Iterativereconstruction may be suitable for certain implementations of the SPECTsystem 10 due, for example, to its speed and the ability to tradeoffreconstruction resolution and noise by varying the convergence andnumber of iterations.

While in the illustrated embodiment, the control module 16 (includingthe data acquisition module 34 and the motor controller 32) and theimage reconstruction and processing module 18 are shown as being outsidethe detector assembly 14 and the operator workstation 20. In certainother implementations, some or all of these components may be providedas part of the detector assembly 14, the operator workstation 20, and/orother components of the SPECT system 10.

Those of ordinary skill in the art will appreciate that the performanceof the SPECT system 10 is at least partially based on the collimatorassembly selected for use therewith. By way of example, systemresolution and sensitivity may be traded off along a collimatorperformance curve for the SPECT system 10. Different configuration ofcollimator and detector assemblies could have different performancecurves, for example. In some instances, a collimator assembly may bedesigned to operate at only a single operating point on theresolution-sensitivity tradeoff curve. Different applications, however,may benefit from operating with different tradeoffs on the performancecurve. To provide different resolutions and sensitivities, multipleswappable collimator assemblies may be provided for each SPECT systemwith each collimator assembly having a different performance point.However, this may add undesired expense and complexity associated withobtaining, storing and swapping the collimator assemblies.

An embodiment of the present technique provides a collimator assembly 12that reduces the need for multiple collimator assemblies. In accordancewith embodiments of the present technique, the collimator assembly 12has one or more adjustable apertures therein. In general, the one ormore adjustable apertures in the collimator assembly 12 have an aperturesize that is adjustable. The adjustable apertures in the collimatorassembly 12 may include pinhole apertures, slit apertures, or acombination thereof. By adjustment of the aperture size of the one ormore adjustable apertures in the collimator assembly 12, the resolutionand/or sensitivity of the SPECT system 10 may be changed without theneed for additional collimator assemblies.

Moreover, the collimator assembly 12 may be configured to allowadjustment of the aperture size during an examination. This may bedesirable, for example, so that multiple scans of the subject 28 may beperformed with different resolutions and sensitivities. In certainembodiments, aperture size may be adjusted during the examinationwithout the need for removal of the subject 28 from the SPECT system 10.Accordingly, the collimator assembly 12 may be configured to allow foraperture adjustment without removal of the subject 28 from the SPECTsystem 10. In one embodiment, the aperture adjustment may be automated.The capability to adjust collimator performance during an examinationenables adaptive SPECT methods, wherein performance of the SPECT systemcan be adapted in an optimal way to the specific imaging task andspecific subject. By way of example, a first image (e.g., a “scoutimage”) may be acquired in a configuration of higher sensitivity andlower resolution. In certain exemplary embodiments, the first image maybe of a heart. Then, depending on the specific subject position, size,shape and distribution of gamma-ray attenuating tissues, the collimatorconfiguration may be adjusted, for example, to provide optimumsensitivity and resolution for the imaging task, such as identificationof myocardial infarcation or the measurement of myocardial perfusion orventricular ejection fraction. A second image may then be obtainedduring the same examination without removal of the subject 28. Based onthe optimum sensitivity and resolution, this second image may be at ahigher resolution but lower sensitivity than the first image. In anotherexample, a first image may be obtained with a short acquisition time toadjust the positioning and focusing of the imaging system 10 on theparticular organ/part of the subject 28. Then, a second image of higherquality may be acquired, often at a longer duration. In this manner, theimaging system 10 can be optimized for each subject based on therequirements of the desired imaging task.

II. Exemplary Pinhole Aperture Collimator Embodiments

Referring now to FIG. 2, an exemplary collimator assembly 12 having oneor more adjustable pinhole apertures 40 is illustrated, in accordancewith embodiments of the present technique. In the illustratedembodiment, a detector assembly 14 encircles the collimator assembly 12.As illustrated, a portion of the detector assembly 14 is removed toillustrate the components of the collimator assembly 12, particularlythe one or more pinhole apertures 40.

In general, gamma rays aligned with the pinhole apertures 40 should passthrough the collimator assembly 12, while gamma rays that are notaligned with the pinhole apertures 40 should be absorbed by thecollimator assembly 12. In the illustrated embodiment, the pinholeapertures 40 in the collimator assembly 12 are arranged in two staggeredrows. The pinhole apertures 40, however, may be arranged in thecollimator assembly 12 in a variety of different configurations. By wayof example, the pinhole apertures may be arranged in the collimatorassembly in even rows. In exemplary embodiments, the pinhole apertures40 may be arranged in the collimator assembly 12 in one, two, three, ormore rows or in other ordered or pseudo-random patterns. Those ofordinary skill in the art will appreciate that the pinhole apertures 40generally define a three-dimensional cone-beam imaging geometry. Whilethe pinhole apertures 40 are illustrated as having a generally circularconfiguration, those of ordinary skill in the art will appreciate thatthe pinhole apertures 40 may have any suitable geometry. By way ofexample, the pinhole apertures 40 may be configured as having apertureconfigurations that are substantially polygonal (e.g., three-sided,four-sided, five-sided, six-sided, and so forth), or substantiallycurved (e.g., elliptical, circular, and so forth).

Those of ordinary skill in the art will appreciate that the resolutionand sensitivity of the SPECT system 10 is based in part on thecross-sectional area of the adjustable pinhole apertures 40. In general,the pinhole apertures 40 may have the same or different aperture sizes.By way of example, the pinhole apertures 40 may have two or moredifferent cross-sectional areas. Furthermore, as described above, theone or more pinhole apertures 40 have an aperture size that isadjustable. In one exemplary embodiment, the aperture size of thepinholes apertures 40 may be adjusted independently. In anotherexemplary embodiment, the aperture size of the pinhole apertures 40 maybe collectively adjusted. In exemplary embodiments, each of the pinholeapertures 40 may be adjusted to a variety of different widths, forexample, from about 0.1 mm to about 10 mm, typically in the range offrom about 1 mm to about 5 mm. Further, in certain embodiments, thepinhole apertures 40 may have a length that is generally no more thantwo or three times greater than the respective widths. The imagereconstruction algorithm should appropriately model the system responseof the various apertures.

Furthermore, those of ordinary skill in the art will appreciate that theefficiency of gamma ray detection is based on the number of the pinholeapertures 40 in the collimator assembly 12. By way of example, acollimator assembly 12 configured to have a large number of the pinholeapertures 40 would typically require less or no rotation to obtain asufficient number of angular projections for image reconstruction.Accordingly, the number of the pinhole apertures 40 may be adjusted toprovide the desired imaging sensitivity for a desired imaging time.Those of ordinary skill in the art will appreciate that the number andspacing of the pinhole apertures 40 should be chosen with considerationof the efficient utilization of the detector assembly 14 and theperformance of the image reconstruction and processing module 18. Forexample, limited overlap of gamma ray lines of response impacting on thedetector assembly 14 may be acceptable.

FIGS. 3-6 illustrate one technique for implementing a collimatorassembly 12 having one or more adjustable pinhole apertures 40 therein,in accordance with exemplary embodiments of the present technique.Referring now to FIG. 3, an exploded view of an example collimatorassembly 12 having one or more adjustable pinhole apertures 40 thereinis illustrated, which may be configured in accordance with exemplaryembodiments of the present technique. In the illustrated embodiment, thecollimator assembly 12 includes an inner pinhole aperture collimator 42having one or more inner pinhole apertures 44 therein and an outerpinhole aperture collimator 46 having one or more outer pinholeapertures 48. While FIG. 3 is an exploded view, the collimator assembly12 may be assembled so that the inner pinhole aperture collimator 42 isdisposed closer to the field of view (e.g., field of view 26 on FIG. 1)than the outer pinhole aperture collimator 46.

Moreover, the collimator assembly 12 should be configured so that eachof the one or more inner pinhole apertures 44 in the inner pinholeaperture collimator 42 are aligned with a respective one of the one ormore outer pinhole apertures 48 in the outer pinhole aperture collimator46 to define the one or more adjustable apertures 40 in the collimatorassembly 12. The aperture size of the one or more adjustable apertures40 thus defined may be adjusted by relative movement of the innerpinhole aperture collimator 42 and the outer pinhole aperture collimator46. By way of example, the inner pinhole aperture collimator 42 mayrotate with respect to the outer pinhole aperture collimator 46, or viceversa, to adjust the aperture size of the adjustable pinhole apertures40. Alternatively, the inner pinhole aperture collimator 42 and theouter pinhole aperture collimator 46 may counter-rotate to adjust theaperture size of the adjustable pinhole apertures 40.

The inner pinhole aperture collimator 42 includes one or more innerpinhole apertures 44 therein. While the inner pinhole apertures 44 areillustrated as having a generally square configuration, those ofordinary skill in the art will appreciate that the inner pinholeapertures 44 may have any suitable geometry. By way of example, theinner pinhole apertures 44 may be configured as having apertureconfigurations that are substantially polygonal (e.g., three-sided,four-sided, five-sided, six-sided, and so forth), or substantiallycurved (e.g., elliptical, circular, and so forth). Further, the innerpinhole aperture collimator 42 is illustrated as being generallycylindrically shaped. Accordingly, the inner pinhole aperture collimator42 includes cylindrical body 50 having the one or more inner pinholeapertures 44 therein. Those of ordinary skill in the art willappreciate, however, that the present technique encompasses pinholeaperture collimators that are not generally cylindrically shaped. Aswill be discussed in more detail below, the inner pinhole aperturecollimator 42 further includes an alignment pin 52. In the illustratedembodiment, the alignment pin 52 extends radially from the cylindricalbody 50.

The outer pinhole aperture collimator 46 includes one or more outerpinhole apertures 48 therein. While the outer pinhole apertures 48 areillustrated as having a generally square configuration, those ofordinary skill in the art will appreciate that the outer pinholeapertures 48 may have any suitable geometry. By way of example, theouter pinhole apertures 48 may be configured as having apertureconfigurations that are substantially polygonal (e.g., three-sided,four-sided, five-sided, six-sided, and so forth), or substantiallycurved (e.g., elliptical, circular, and so forth). Further, the outerpinhole aperture collimator 46 is illustrated as being generallycylindrically shaped. Accordingly, the outer pinhole aperture collimator46 includes cylindrical body 54 having the one or more pinhole apertures48 therein. Those of ordinary skill in the art will appreciate, however,that the present technique encompasses pinhole aperture collimators thatare not generally cylindrically shaped. For instance, in anotherembodiment the inner pinhole apertures 44 and the outer pinholeapertures 48 may be rotated about 45 degrees such that the diagonal ofthe square-shape aperture is aligned with the longitudinal axis and theinner pinhole aperture collimator 42 and the outer pinhole aperturecollimator 46 are elliptically shaped to more closely follow the humanbody's contour. As will be appreciated, elliptically shaped collimatorwill not be able to rotate with respect to one another so that may beconfigured to slide axially relative to each other to adjust the size ofthe pinhole. This technique is not limited to square-shaped pinholeapertures. In this particular embodiment, the rotated square pinholes(rhombus) allow isotropic adjustment of the aperture size in both axialand tangential directions while preserving the square shape.

As will be discussed in more detail below, the outer pinhole aperturecollimator 46 further includes an alignment slot 56. In the illustratedembodiment, the alignment slot 56 is sized so that the alignment pin 52of the inner pinhole aperture collimator 42 may be moveably disposedtherein. Those of ordinary skill in the art will appreciate that the useof the alignment pin 52 and the alignment slot 56 represents one of manysuitable techniques for maintaining the desired alignment between theinner pinhole apertures 44 of the outer pinhole aperture collimator 42and the outer pinhole apertures 48 of the outer pinhole aperturecollimator 46. By way of example, both the inner pinhole aperturecollimator 42 and the outer pinhole aperture collimator 46 may beindependently mounted on collimator supports capable of rotating either,or both, collimators. In such an embodiment, the use of the alignmentpin 52 and the alignment slot 56 may not be necessary.

Further, the inner and outer pinhole aperture collimators 42 and 46 maybe mechanically coupled or placed in contact with each other so as torotate together, or they may be decoupled so as to rotate separately. Inexemplary embodiments, the collimator assembly 12 may be configured tolimit movement of the inner pinhole aperture collimator 42 and the outerpinhole aperture collimator 46 with respect to one another. By limitingtheir respective movement, each of the pinhole apertures 44 in the innerpinhole aperture collimator 42 may remain at least partially alignedwith a respective one of the pinhole apertures 48 in the outer pinholeaperture collimator 46. In the illustrated embodiment, the inner pinholeaperture collimator 42 includes an alignment pin 52 that extendsradially from the cylindrical body 50 of the inner pinhole aperturecollimator 42. The alignment pin 52 is configured to be moveablydisposed in the corresponding alignment slot 56 in the cylindrical body54 of the outer pinhole aperture collimator 46. Accordingly, thealignment pin 52 may be configured to maintain the alignment of theinner pinhole apertures 44 and the outer pinhole apertures 48.Furthermore, the alignment pin 52 illustrated in FIG. 3 is part of theinner pinhole aperture collimator 42 and the alignment slot 56 is partof the outer pinhole aperture collimator 46. Alternatively, thealignment pin 52 may be part of the outer pinhole aperture collimator46, and the alignment slot 56 may be part of the inner pinhole aperturecollimator 42, for example.

Referring now to FIGS. 4 and 5, a portion of the inner pinhole aperturecollimator 42 and a portion the outer pinhole aperture collimator 46 areillustrated in accordance with exemplary embodiments of the presenttechnique. In the illustrated embodiment, an inner pinhole aperture 44 ain the inner pinhole aperture collimator 42 is aligned with a respectiveouter pinhole aperture 48 a in the outer pinhole aperture collimator 46to define an adjustable aperture 40 a in the collimator assembly 12. Aspreviously mentioned, movement of at least one of the inner pinholeaperture collimator 42 or the outer pinhole aperture collimator 46should adjust the aperture size of the pinhole aperture 40 a. Asillustrated, movement of the outer pinhole aperture collimator 46 in thedirection 58 indicated by the arrow adjusts the aperture size of thepinhole aperture 40 a. In the illustrated embodiment, the direction 58of the movement is diagonal with respect to the inner and outer pinholeapertures 44 a and 48 a. Accordingly, while the aperture size of theadjustable pinhole aperture 40 a is adjusted, the pinhole aperture 40 amaintains its square shape due to this diagonal movement. Those ofordinary skill in the art will appreciate that movement in directionsother than diagonal are encompassed by the present technique.

As illustrated by FIG. 4, when the inner pinhole aperture 44 a and theouter pinhole aperture 48 a are axially aligned and tangentiallyaligned, the adjustable pinhole aperture 40 a defined thereby has itsmaximum aperture size. However, as illustrated by FIG. 5, axialdisplacement of the inner and outer pinhole apertures 44 a and 48 bresults in an adjustable pinhole aperture 40 a in the collimatorassembly 12 of reduced size. As previously mentioned, the alignment pin52 in the inner pinhole aperture collimator 42 may limit the movement ofthe inner pinhole aperture collimator 42 and/or the outer pinholeaperture collimator 46, thus limiting both axial and tangentialdisplacement of the inner and outer pinhole apertures 44 a and 48 b.

Referring now to FIG. 6, a perspective, cut-away view of the collimatorassembly 12 is provided to illustrate the alignment of the inner andouter pinhole apertures 44 and 48, in accordance with exemplaryembodiments of the present technique. In the illustrated embodiment, aninner pinhole aperture collimator 42 having one or more inner pinholeapertures 44 therein is disposed within an outer pinhole aperturecollimator 46 having one or more outer pinhole apertures 48. Asillustrated, the inner and outer pinhole apertures 44 and 48 align todefine one or more adjustable apertures 40 in the collimator assembly12.

In the embodiment of FIG. 6, the outer pinhole apertures 48 open in theshape of a square pyramid to the exterior surface 60 of the outerpinhole aperture collimator 46, and the inner pinhole apertures 44 openin the shape of a pyramid to the inner surface 62 of the inner pinholeaperture collimator 42. With this configuration, gamma rays traveling ina direction oblique to the adjustable pinhole apertures 40 may passthrough the collimator assembly 12. Accordingly, gamma rays that passthrough the adjustable pinhole apertures 40 would have a square-beamgeometry. Gamma rays not aligned with the adjustable pinhole apertures40 would not pass through the collimator assembly 12. While the innerand outer pinhole apertures 44 and 48 are illustrated as opening in theshape of a pyramid, those of ordinary skill in the art will appreciatethat other configurations are encompassed by the present technique. Byway of example, the inner and outer pinhole apertures 44 and 48 may openin the shape of a circular cone, for example, if the inner and outerpinhole apertures 44 and 48 have a generally circular configuration.

FIGS. 7-14 illustrate an alternative technique for implementing acollimator assembly 12 having one or more adjustable pinhole apertures40 therein, in accordance with exemplary embodiments of the presenttechnique. Referring now to FIGS. 7 and 8, an exemplary diaphragm 64that includes a plurality of blocks 66 a-66 d arranged to define anadjustable pinhole aperture 40 a is illustrated. As will be discussed inmore detail below with respect to FIG. 14, the diaphragm 64 may beimplemented in a collimator assembly 12 to provide a collimator assembly12 with one or more adjustable pinhole apertures 40. Moreover, thediaphragm 64 is configured so that positioning of the blocks 66 a-66 dwith respect to one another adjusts the aperture size of the adjustablepinhole aperture 40 a.

In illustrated embodiment, the diaphragm 64 includes four blocks 66 a-66d that are arranged to define an adjustable pinhole aperture 40 a havinga generally square configuration. As illustrated, blocks 66 a and 66 care arranged in parallel and spaced a distance apart to define first andsecond parallel sides 68 and 70 of the adjustable pinhole aperture 40 a.Moreover, blocks 66 b and 66 d are also arranged in parallel and spaceda distance apart to define third and fourth parallel sides 72 and 74 ofthe adjustable pinhole aperture 40 a. In general, blocks 66 b and 66 dare generally perpendicular to blocks 66 a and 66 c. While FIGS. 7 and 8illustrated four blocks 66 a-66 d defining a square aperture, any numberof blocks may be used and arranged to define an adjustable aperture witha variety of different configurations, including aperture configurationsthat are substantially polygonal (e.g., three-sided, four-sided,five-sided, six-sided and so forth), or substantially curved (e.g.,elliptical, circular and so forth).

As previously mentioned, the positioning of blocks 66 a-66 d withrespect to one another adjusts the aperture size of the adjustablepinhole aperture 40 a. By way of example, movement of each of the blocks66 a-66 d in the directions 76 a-76 d indicated by the arrows adjuststhe aperture size of the pinhole aperture 40 a. In the illustratedembodiment, the directions 76 a-76 d of the movement are diagonal withrespect to the adjustable pinhole aperture 40 a. In the illustratedembodiment, the directions 76 a-76 d of movement of each of the blocks66 a-66 d is generally at an angle generally parallel to the diagonalsof pinhole aperture 40 a. Accordingly, while the aperture size of theadjustable pinhole aperture 40 a is adjusted, the adjustable pinholeaperture 40 a maintains its square shape due to this diagonal movement.Moreover, each set of two parallel blocks (such as parallel blocks 66 aand 66 c and parallel blocks 66 b and 66 d) is move in an oppositedirection to adjust the size of pinhole aperture 40 a. Similarly, blocks66 b and 66 d are also positioned in generally opposite directions withrespect to each other. Moreover, the diaphragm 64 may be configured sothat parallel blocks 66 a and 66 c are moved in a direction 76 a and 76c that is generally perpendicular to the direction 76 b and 76 d thatparallel blocks 66 b and 66 d are moved. Further, those of ordinaryskill in the art will appreciate that movement of the blocks 66 a-66 din directions other than diagonal are encompassed by the presenttechnique. By way of example, moving the blocks 66 a-66 d from theconfiguration shown in FIG. 7 to that shown in FIG. 8 may beaccomplished by first moving block 66 a upward, block 66 b rightward,block 66 downward, and block 66 d leftward; and then moving block 66 arightward until it touches block 66 b, moving block 66 b downward untilit touches block 66 d, moving block 66 c leftward until it touches block66 d, and moving block 66 d upward until it touches block 66 a. In thismanner, the net diagonal movement may be accomplished via the vector sumof movements in off-diagonal directions, for example,

Referring now to FIG. 9, a side-view of the diaphragm 64 is illustrated.In certain embodiments, adjacent blocks, such as blocks 66 d and 66 cmay be interlocked. In the illustrated embodiment, the edge 78 of thefourth block 66 d is configured to interlock with the adjacent edge 80of the third block 66 c. As illustrated, the edge 78 of the fourth block66 d may have a knife edge that interlocks with the adjacent edge 80 ofthe third block 66 c. As illustrated, the adjacent edge 80 of the thirdblock 66 c may include an angled recess configured to accept the edge 78of the fourth block 66 d. Those of ordinary skill in the art willappreciate that the interlocking of adjacent blocks 66 a-66 d of thediaphragm 64 should facilitate the absorption of gamma rays that are notaligned with the adjustable pinhole aperture 40 a but are aligned withthe intersection of adjacent blocks. Moreover, to permit theirpositioning, the blocks 66 a-66 d may be slidably interlocked. Asillustrated, blocks 66 c and 66 d are slidably interlocked. Accordingly,blocks 66 c and 66 d may be positioned to allow for adjustment of theaperture size of the adjustable pinhole aperture 40 a.

Those of ordinary skill in the art will appreciate that the apertureedge of the adjustable pinhole aperture 40 a may be defined, forexample, by the edges of the blocks 66 a-66 d. By way of example, anaperture edge (e.g., fourth parallel side 74 on FIG. 7) may be definedby edge 78 of the fourth block 66 d, illustrated as a knife edge. WhileFIG. 9 illustrates the blocks 66 a-66 d as having a knife-edgeconfiguration, other aperture-edge configurations may also be suitable.Those of ordinary skill in the art will appreciate that theaperture-edge configuration may be selected based on, inter alia, thedesired point-spread-function response. Further, the aperture edges maybe constructed from the same or different material as that used for theblocks 66 a-66 d, which may contain a radiation-absorbent material (e.g.lead or tungsten). By way of example, the aperture edges may be made ofor coated with gold, tungsten or iridium based, in part, on the desiredgamma-ray penetration and x-ray fluorescence properties of the apertureedge.

FIG. 10 illustrates a cross-sectional, side view of the diaphragm 64having an alternative aperture-edge configuration, in accordance with anembodiment of the present technique. As illustrated, the aperture edge(e.g., fourth parallel side 74 on FIG. 7) is defined by edge 78 of thefourth block 66 d, illustrates as a round edge. Moreover, the adjacentedge 80 of the third block 66 c may be configured to interlock with theedge 78 of the fourth block 66 d having a round end. As illustrated, theadjacent edge 80 of the third block 66 c that includes a rounded recess80 configured to accept the edge 78 of the fourth block 66 d.

Referring now to FIG. 11, an exemplary block 66 d of the diaphragm 64 ofFIGS. 7 and 8 is illustrated, in accordance with an embodiment of thepresent technique. In the illustrated embodiment, block 66 d has an edge78 with a knife edge. As previously mentioned, the edge 78 defines theaperture edge (e.g., fourth parallel side 74 on FIG. 7) and interlockswith the adjacent edge 80 of block 66 c. Moreover, block 66 d also hasanother edge with an angled recess 82. The angled recess 82 of block 66d may interlock with an edge of the first block 66 a that defines anaperture edge (e.g., first parallel side 68 on FIG. 7). Block 66 d mayfurther include one or more pins 84 that extend from a surface 86 of theblock 66 d. In one exemplary embodiment, each of the pins 84 may becoupled to the body of the block 66 d to transfer force from an actuatorto the block 66 d to move the block 66 d. Those of ordinary skill in theart should recognize that there are alternative methods that may beutilized to transfer force from an actuator to the block to move it to adesired position.

As previously mentioned, movement of each of the blocks 66 a-66 d in thedirections 76 a-76 d indicated by the arrows adjusts the aperture sizeof the adjustable pinhole aperture 40 a. A number of different actuatorsmay be used to operate the diaphragm 64. By way of example, any of avariety of different mechanism may be used to position the blocks 66a-66 d with respect to one another to adjust the aperture size of theadjustable pinhole aperture 40 a, including, for example, a lever-armmechanism, a rack and pinion mechanism, and so forth.

Referring now to FIGS. 12 and 13, an actuator is illustrated foroperating the diaphragm 64. In the illustrated embodiment, the actuatorincludes a lever-arm mechanism configured to move each of the blocks 66a-66 d with respect to one another. As illustrated, the lever-armmechanism includes plate 88, ring 92 and lever 96. Each of the blocks 66a-66 d may be coupled to plate 88. Plate 88 includes one or more slots90 therein. The pins 84 in each of the blocks 66 a-66 d extend from thesurface (e.g., surface 86 on FIG. 11) of the respective block throughthe corresponding slot. Each of the slots 90 may be sized to define therange of motion of the corresponding block. By way of example, each ofthe slots 90 may be configured to allow the blocks 66 a-66 d to move inthe directions 76 a-76 d indicated on FIGS. 7 and 8.

In certain embodiments of the present technique, the ring 92 of thelever-arm mechanism may be coupled, for example, to the plate 88. In oneexemplary embodiment, the ring 92 may be rotateably coupled to the plate88 so that the ring 92 can rotate with respect to the plate 88. Asillustrated, the ring 92 may include one or more openings 94 therein forplacement of a corresponding one of the pins 84. In the illustratedembodiment, the pins 84 in each of the blocks 66 a-66 d extend from thesurface (e.g., surface 86 on FIG. 11) of the respective block through acorresponding one of the slots 90 in the plate 88 and into acorresponding one of the openings 94 in the ring 92. Each of theopenings 94 in the ring 92 may be sized so that rotation of the ring 92will transfer force to one or more of the pins 84 extending into acorresponding one of the openings 94. In the embodiment illustrated inFIG. 13, certain of the openings 94 are rounded and certain are slotted,wherein the rounded openings are intended for clearance only to allowfree movement of the pins 84 inserted therethrough while the slottedopenings transmit the force onto the pins 84 as the lever 96 isactuated. For example, the ring 92 may be configured so that sufficientforce is transferred to the ring 92 from the lever 96 so that the blocks66 a-66 d may move with respect to one another, thus adjusting theaperture size of the pinhole aperture 40 a. Further, the ring 92 alsomay include a central opening 98 therein that is aligned with theadjustable pinhole aperture 40 a, for example. In the embodimentillustrated in FIG. 13, the central opening 98 is larger than themaximum desired aperture size of the pinhole aperture 40 a to allowunimpeded passage of gamma rays aligned with the pinhole aperture 40 a.

The lever 96 of the lever-arm mechanism may be coupled to the blocks 66a-66 d. In the illustrated embodiment, the lever 96 may be indirectlycoupled to the blocks 66 a-66 d via ring 92. As illustrated, the lever96 may be coupled to the ring 92. In general, the lever 96 and the ring92 may be configured so that movement of the lever 96 rotates the ring92. As the ring 92 rotates, force may be transferred from the lever 96to the one or more of the pins 84 of the blocks 66 a-66 d to move theblocks 66 a-66 d with respect to one another. In general, the lever 96may have a range of motion to allow the desired adjustment of theaperture size of the pinhole aperture 40 a.

As previously mentioned, the diaphragm 64 discussed above with respectto FIGS. 7-13 may be implemented to provide a collimator assembly 12with one or more adjustable pinhole apertures 40 therein. Referring nowto FIG. 14, a collimator 12 is illustrated having one or more diaphragms64 implemented therein, in accordance with an embodiment of the presenttechnique. In the illustrated embodiment, each of the one or morediaphragms 64 defines a corresponding adjustable pinhole aperture in thecollimator assembly 12. As illustrated, the collimator assembly 12 mayinclude a collimator body 100 having one or more openings 102 therein.In the illustrated embodiment, the collimator body 100 serves a dualpurpose, as a structure to support each diaphragm 64 and tosubstantially absorb gamma rays. While the collimator body 100 may takenany of a number of shapes, the collimator body 100 is depicted asgenerally cylindrical in shape and having a plurality of openings 102therein. In exemplary embodiments, the openings 102 in the collimatorbody 100 have an aperture size large than the largest desired aperturesize of the adjustable pinhole apertures 40, for example, to allowunimpeded passage of gamma rays aligned with the pinhole apertures 40.

As described above, each of the diaphragms implemented into thecollimator assembly 12 may include a plurality of blocks arranged toform an adjustable pinhole aperture. For example, diaphragm 64 includesfour blocks 66 a-66 d that are arranged to form adjustable pinholeaperture 40 a. Moreover, each of the diaphragms may be arranged in thecollimator assembly 12 so that each of the adjustable pinhole apertures40 (such as pinhole aperture 40 a on FIG. 14) is aligned with acorresponding one of the openings 102 in the collimator body 100.Accordingly, gamma rays that are aligned with the adjustable pinholeapertures 40 pass through the openings 102 and do not contact thecollimator body 100. In the illustrated embodiment, each of the blocksthat define one of the adjustable pinhole apertures 40 is coupled to acorresponding plate. By way of example, blocks 66 a-66 d may be coupledto the plate 88. Further, the plate 88 may be coupled to an innersurface 104 of the collimator body 100. The plate 88 may be positionedin the collimator assembly 12 to align each of the adjustable pinholeapertures 40 with a corresponding one of the openings 102 in thecollimator body 100.

In accordance with exemplary embodiments, any suitable actuator may beutilized for operating each of the diaphragms (e.g., diaphragm 64) inthe collimator assembly. In the illustrated embodiment, the actuatorincludes a lever-arm mechanism coupled to an actuator ring 106. Asillustrated, each of the diaphragms includes a corresponding levercoupled to blocks defining the adjustable pinhole aperture. By way ofexample, lever 96 may be coupled to blocks 66 a-66 d, as describedabove. Each of the levers (e.g., lever 96) may be coupled to theactuator ring 106. Accordingly, movement of the actuator ring 106results in corresponding movement of the levers. As described above, thelevers may be coupled to the blocks defining the adjustable pinholeapertures so that movement of the levers results in a correspondingmovement of the blocks and thus an adjustment of the aperture size. Byway of example, movement of the actuator ring 106 should result inmovement of the lever 96, thus resulting in movement of the blocks 66a-66 d with respect to one another. The blocks 66 a-66 d should bearranged so that movement thereof results in adjusting the aperture sizeof the adjustable pinhole aperture 40 a. In another embodiment, theactuating mechanism may involve the rings 106 and the lever 96 decoupledfrom the ring 92. The lever 96 may be placed with a rack rod, and thering 92 may function as a pinion (round edge replaced with a gearshape). Thus, by pushing on the ring 96 in the direction of the mainaxis of the collimator assembly 12, the rack and pinion mechanism thatincludes the rod 96 and gear on the ring 92 will actuate ring 92 and, inturn, will actuate on pins 84 to effectuate movement of blocks 66 a-66d.

III. Exemplary Slit Aperture Collimator Embodiments

While the preceding discussion of FIGS. 2-14 has described adjustablepinhole aperture collimators, the present technique is also applicableto slit aperture collimator. Referring now to FIG. 15, a perspectiveview of the collimator assembly 12 with a detector assembly 14encircling the collimator assembly 12 is provided, in accordance withexemplary embodiments of the present technique. As illustrated, aportion of the detector assembly 14 is removed to illustrate thecomponents of the collimator assembly 12, particularly the one or moreslit apertures 108 and the one or more septa 110. In general, thecollimator assembly 12 and the one or more septa 110 may be arrangedsuch that the one or more slit apertures 108 and the one or more septa110 define one or more pathways for gamma rays emanating from a subjectplaced in the field of view 26. Gamma rays aligned with one of theslit/septa pathways should pass through the collimator assembly 12,while gamma rays that are not aligned with one of the slit/septapathways should not pass through the collimator assembly. Those ofordinary skill in the art will appreciate that the slit apertures 108and the septa 110 generally define a two-dimensional fan-beam imaginggeometry wherein the septa 100 generally define transaxial slices.

As illustrated, the slit apertures 108 may extend in a directiongenerally parallel to the longitudinal axis 112 of the collimatorassembly 12. In addition, the collimator assembly 12 may include one ormore sections spaced around the longitudinal axis 112 of the collimatorassembly 12 such that spaces between the sections define the slitapertures 108. By way of example, the spaced sections may be or includeone or more panels 114 spaced around the longitudinal axis 112 of thecollimator assembly 12 so as to define the slit apertures 108.

Moreover, the slit apertures 108 are referred to as generally onedimensional because the length of a slit aperture 108 is typically longin comparison to the width of the slit aperture 108. For example, thelength of a slit aperture 108 may be four, five, ten, or more timesgreater than the respective width of the slit aperture 108.

For support, the panels 114 may be coupled by a mechanical couplingmechanism, such as bands (rings) 116 illustrated on FIG. 15. By way ofexample, each of the bands 116 may be coupled to each of the panels 114at the respective ends of the collimator assembly 12. As illustrated,the bands 116 may be configured to hold the panels 114 in a generallycylindrical arrangement. Alternatively, a collar or other suitableassembly may be used to hold the panels 114 in the desired arrangement.Further, while the panels 114 are illustrated in FIG. 2 as curvedsections, the present technique encompasses the use of sections that arenot curved. In addition, while the panels 114 of the collimator assembly12 are illustrated as separate sections, the present techniqueencompasses the use of a collimator assembly 12 that is unitary. Thatis, the collimator assembly 12 may be fabricated as a solid piece havingone or more slit apertures 108 therein. Furthermore, in certainexemplary embodiments, the collimator assembly 12 may be constructed asa unitary piece in which the slit apertures 108 are filled by a materialthat provides mechanical support but that also allows most gamma rays topass through the slit apertures 108 without interaction.

As previously mentioned, one or more septa 110 may be spaced on a sideof the collimator assembly 12 opposite from the field of view 26. In theillustrated embodiment, each of the septa 110 is generallyannular-shaped and spaced along the longitudinal axis 112 of thecollimator assembly 12. The septa 110 may be arranged, for example, toprovide the desired slice information for the SPECT system 10. Asillustrated, the septa 110 are generally parallel to each other andgenerally perpendicular to the longitudinal axis 112 of the collimatorassembly 12. In this embodiment, the septa 110 may define the axialslice information for the SPECT system 10 while the adjustable slitapertures 108 provide the transaxial information. Those of ordinaryskill in the art will appreciate that the septa 110 may also be arrangedin a generally converging or diverging configuration to alter the slicedefinition by either magnifying or minifying the axial field of view.

Those of ordinary skill in the art will appreciate that the resolutionand sensitivity of the SPECT system 10 is based in part on the width ofthe adjustable slit apertures 108 and the septa 110 spacing. In general,the width of the adjustable slit apertures 108 and the septa 110 spacingmay be the same or different, with different widths providing differentresolving power. By way of example, the adjustable slit apertures 108and the spacing between each of the septa 110 may have two or moredifferent widths. As previously mentioned, the adjustable slit apertures108 have aperture sizes that are adjustable. In exemplary embodiments,the adjustable slit apertures 108 may be adjusted to a variety ofdifferent widths, for example, in the range of from about 0.1 mm toabout 10 mm, and typically in the range of from about 1 mm to about 5mm. Furthermore, the adjustable slit apertures 108 may be configured forcollective and/or independent adjustment. Adjustment of the adjustableslit apertures 108 to have different widths may provide widths withdifferent resolving power and sensitivities. By differing the aperturesize of the adjustable slit apertures 108, the spatial resolution andsensitivities of the SPECT system 10 may be changed. In certainembodiments, the spacing between the septa 110 may have a width in therange of from about 0.1 mm to about 10 mm, and typically in the range offrom about 1 mm to about 5 mm. The various adjustable slit apertures 108and septa 110 spacing may have a distribution of sizes, and thusdiffering spatial resolutions and sensitivities. The imagereconstruction algorithm should appropriately model the system responseof the various apertures.

Furthermore, those of ordinary skill in the art will appreciate that theefficiency of gamma ray detection is based on the number of slitapertures 108 in the collimator assembly 12. By way of example, acollimator assembly 12 configured to have a large number of slitapertures 108 would typically require less or no rotation to obtain asufficient number of angular projections for image reconstruction.Accordingly, the number of the slit apertures 108 may be adjusted toprovide the desired imaging sensitivity for a desired imaging time.Those of ordinary skill in the art will appreciate that the number andspacing of the slit apertures 108 should be chosen with consideration ofthe efficient utilization of the detector assembly 14 and theperformance of the image reconstruction and processing module 18. Forexample, limited overlap of gamma ray lines of response impacting on thedetector assembly 14 may be acceptable.

While the preceding discussion of FIG. 15 has described the slitapertures in the collimator assembly as having slit apertures 108extending in a direction generally parallel to the longitudinal axis 112of the collimator assembly 12, and the septa 110 spaced along thelongitudinal axis 112 of the collimator assembly 12, one of ordinaryskill in the art will recognize that the present technique may beimplemented with collimator assemblies having alternative slitconfigurations. By way of example, the slit apertures 108 may extend ina direction generally perpendicular to the longitudinal axis 112 of thecollimator assembly 12 while the septa 110 may extend longitudinally andradially from the collimator assembly 12. In another exemplaryembodiment, the slit apertures 108 may extend in a direction generallydiagonal to the longitudinal axis 112 of the collimator assembly 12, forexample, the slit apertures 108 may follow spirals.

FIGS. 16-18 illustrate one technique for implementing a collimatorassembly 12 having one or more adjustable slit apertures 108 therein, inaccordance with exemplary embodiments of the present technique.Referring now to FIG. 16, an exploded view of an example collimatorassembly 12 having one or more slit apertures 108 therein isillustrated, which may be configured in accordance with exemplaryembodiments of the present technique. In the illustrated embodiment, thecollimator assembly 12 includes an inner cylindrical slit collimator 118and an outer cylindrical slit collimator 120. While FIG. 16 is anexploded view, the collimator assembly 12 may be assembled so that theinner cylindrical slit collimator 118 is disposed closer to a volume(such as field of view 26 on FIG. 15) than the outer cylindrical slitcollimator 120. As will be described in more detail below, the innercylindrical slit collimator 118 and the outer cylindrical slitcollimator 120 each include a plurality of overlapping panels, such asinner panels 122 and outer panels 124, wherein spaces between adjacentinner and outer panels 122 and 124 define the adjustable slit apertures108, as illustrated by FIGS. 17-18. In general, the inner cylindricalslit collimator 118 and the outer cylindrical slit collimator 120 shouldbe configured so that relative rotation of the inner cylindrical slitcollimator 118 and the outer cylindrical slit collimator 120 adjusts theaperture size of the adjustable slit apertures 108. By way of example,the inner cylindrical slit collimator 118 may rotated with respect tothe outer cylindrical slit collimator 120 or vice versa.

The inner cylindrical slit collimator 118 includes a plurality of innerpanels 122 spaced at least partially around the longitudinal axis 112 ofthe collimator assembly 12. In the illustrated embodiment, the innerpanels 122 extend in a direction generally parallel to the longitudinalaxis 112 of the collimator assembly 12. Further, each of the innerpanels 122 includes a thinned portion 128 extending along the length ofthe respective panel. In general, the thinned portion 128 of arespective panel has a thickness less than the remainder of the panel.As illustrated, the inner panels 122 are spaced around the longitudinalaxis 112 of the collimator assembly 12 such that the thinned portion 128of the inner panels 122 are not adjacent to one another. For support,the inner panels 122 may be coupled by any suitable mechanical couplingmechanism, such as bands (rings) or collars (not illustrated). By way ofexample, bands may be coupled to each of the inner panels 122 at therespective ends of the collimator assembly 12. In exemplary embodiments,the bands may be configured to hold the inner panels 122 in a generallycylindrical arrangement. Further, while the inner panels 122 areillustrated in FIG. 16 as curved sections, the present techniqueencompasses the use of panels that are not curved.

The outer cylindrical slit collimator 120 includes a plurality of outerpanels 124 spaced at least partially around the longitudinal axis 112 ofthe collimator assembly 12. In the illustrated embodiment, the outerpanels 124 extend in a direction generally parallel to the longitudinalaxis 112 of the collimator assembly 12. Further, each of the outerpanels 124 includes a thinned portion 130 extending along the length ofthe respective panel. In general, the thinned portion 130 of arespective panel has a thickness less than the remainder of the panel.As illustrated, the outer panels 124 are spaced around the longitudinalaxis 112 of the collimator assembly 12 such that the thinner portion 130of the outer panels 124 are not adjacent to one another. For support,the outer panels 124 may be coupled by any suitable mechanical couplingmechanism, such as bands (rings) or collars (not illustrated). By way ofexample, bands may be coupled to each of the outer panels 124 at therespective ends of the collimator assembly 12. In exemplary embodiments,the bands may be configured to hold the outer panels 124 in a generallycylindrical arrangement. Further, while the outer panels 124 areillustrated in FIG. 16 as curved sections, the present techniqueencompasses the use of panels that are not curved.

As previously mentioned, the inner cylindrical slit collimator 118 andthe outer cylindrical slit collimator 120 may be assembled so thatspaces between adjacent inner and outer panels 122 and 124 define one ormore adjustable slit apertures 108. Referring now to FIGS. 17 and 18, acollimator assembly 12 is illustrated having an inner cylindrical slitcollimator 118 disposed within an outer cylindrical slit collimator 120.In the illustrated embodiment, the inner cylindrical slit collimator 118and the outer cylindrical slit collimator 120 each include a pluralityof overlapping panels, such as inner panels 122 and outer panels 124,wherein spaces between adjacent inner and outer panels 122 and 124define the one or more adjustable slit apertures 108. For example, theinner cylindrical slit collimator 118 and the outer cylindrical slitcollimator 120 should be arranged so that each of the inner panels 122is adjacent to two of the outer panels 124. Each of the inner panels 122should overlap with one of the adjacent outer panels 124. Asillustrated, the thinned portion 128 of one of the inner panels 122overlaps with the thinned portion 130 of one of the outer panels 124.

In addition, the inner cylindrical slit collimator 118 and the outercylindrical slit collimator 120 should be configured so that rotation ofat least one of the inner cylindrical slit collimator 118 or the outercylindrical slit collimator 120 adjusts the aperture size of theadjustable slit apertures 108. In exemplary embodiments, rotation of theinner cylindrical slit collimator 118 with respect to the outercylindrical slit collimator 120, or vice versa, should increase ordecrease the aperture size of the adjustable slit apertures 108. Forexample, clockwise rotation of the inner cylindrical slit collimator 118with respect to the outer cylindrical slit collimator 120 shouldincrease the size of the adjustable slit apertures 108. Moreover,counter-rotation of the inner cylindrical slit collimator 118 and theouter cylindrical slit collimator 120 should also increase or decreasethe aperture size of the adjustable slit apertures 108. Moreover, thewidth of the thinned portions 128 and 130 of the inner and outer panels122 and 124, respectively, may define the range of motion for rotationof at least one of the inner cylindrical slit collimator 118 or theouter cylindrical slit collimator 120. By way of example, rotation ofthe inner cylindrical slit collimator 118 with respect to the outercylindrical slit collimator 120 will be limited by width of the thinnerportions 128 and 130.

FIGS. 19 and 20 illustrate an alternative technique for implementing acollimator assembly 12 having one or more adjustable slit apertures 108therein, in accordance with exemplary embodiments of the presenttechnique. In the illustrated embodiment, the collimator assembly 12 isgenerally cylindrical in shape and has adjustable slit apertures 108therein. The collimator assembly 12 may be configured to have anadjustable diameter, wherein adjustment of the diameter results in acorresponding aperture size adjustment. By way of example, theadjustable slit apertures 108 may have a first aperture size A1 at afirst diameter D1 of the collimator assembly 12 and a second aperturesize A2 at a second diameter D2 of the collimator assembly 12. Inexemplary embodiments, the collimator assembly 12 may be configured sothat dilation of the collimator assembly 12 increases the aperture sizeof the adjustable slit apertures 108 and/or contraction of thecollimator assembly 12 decreases the aperture size of the adjustableslit apertures 108. As illustrated by FIGS. 19 and 20, dilation of thecollimator assembly 12 from a diameter of D1 to a diameter of D2 resultsin a corresponding increase in aperture size from A1 to A2. Those ofordinary skill in the art will appreciate that the technique illustratedby FIGS. 19 and 20 for aperture size adjustment may be implemented witha variety of different slit aperture collimators. For example, thistechnique may be implemented with collimator assembly 12 illustrated onFIG. 15 that includes a plurality of panels 114 arranged to define aplurality of adjustable slit apertures 108. Those of ordinary skill inthe art will appreciate that the combined thickness of the inner andouter panels 112 and 124 should be sufficient to stop gamma rays of thedesired energy for SPECT imaging. In particular, when the panels arerotated to adjust the slit aperture size, a pathway may be exposed inwhich gamma rays would pass only through the thinned section of one ofthe panels. If the thickness of the thinned panel section is notsufficient to stop the gamma rays, then additional radiation absorbentmaterial may be need to block passage of gamma rays not aligned with theslit apertures. This additional material could be added to the outerand/or inner panels 122 and 1234 in the region where the panelstransition from full thickness to thinned thickness, for example, and insuch as way as to not interfere with relative rotation of the collimatorpanels.

FIGS. 21-23 illustrate another alternative technique for implementing acollimator assembly 12 having one or more adjustable slit apertures 108therein, in accordance with exemplary embodiments of the presenttechnique. In the illustrated embodiment, panels 114 a and 114 b defineadjustable slit aperture 108. As previously described and illustrated byFIG. 15, a plurality of panels 114 (e.g., panels 114 a and 114 b) may bearranged at least partially around the longitudinal axis 112 of acollimator assembly 12 and extending in a direction generally parallelthereto with the spaces between the panels 114 defining each adjustableslit aperture 108. Referring again to FIGS. 21-23, the panels 114 may beconfigured such that rotation of the slit edges 134 (e.g., slit edges134 a and 134 b) adjusts the aperture size of the adjustable slitaperture 108, as will be discussed in more detail below,

In the illustrated embodiment, the panels 114 include panel bodies 136(e.g., panel bodies 136 a and 136 b) and slit edges 134. As illustrated,the slit edges 134 are the portion of the panels 114 that are adjacentto the adjustable slit aperture 108. The space between the slit edges134 defines the adjustable slit aperture 108. In exemplary embodiments,the slit edges 134 may have rounded ends 138 (e.g., rounded ends 138 aand 138 b) and knife ends 140 (e.g., knife ends 140 a and 140 b). Therounded ends 138 of the slit edges 134 may overlap with a portion of thepanel bodies 136. In the illustrated embodiment, the rounded ends 138may be configured to mate with a corresponding recess (such as roundedrecesses 142 a and 142 b) of the panel bodies 136. As illustrated therounded recesses 142 of the panel bodies 136 may be at one end of thepanel bodies 136. While FIGS. 22 and 23 illustrate the slit edges 134 ashaving a knife-edge configuration, other aperture edge configurations(e.g., rounded) may also be suitable. Those of ordinary skill in the artwill appreciate that the aperture edge configuration may be selectedbased on, inter alia, the desired point-spread-function response.Further, the slit edges 134 may be constructed from the same ordifferent material as that used for the panel bodies 136, which maycontain a radiation-absorbent material, such as lead or tungsten, forexample.

As previously mentioned, rotation of the slit edges 134 may adjust theaperture size of the adjustable slit aperture 108. By way of example,rotation of at least one of slit edge 134 a or slit edge 134 b shouldadjust the aperture size of the adjustable slit aperture 108. In theillustrated embodiment, rotation of the knife edges 140 of the slitedges 134 adjusts the aperture size of the adjustable slit aperture 108.In exemplary embodiments, the knife edges 140 rotate with respect to thecorresponding rounded ends 138. As illustrated, the knife edges 140rotate about an axis of rotation, illustrated on FIGS. 22 and 33 as pins144. Pins 144 may extend at least partially through the length of theslit edges 134. In exemplary embodiments, pins 144 may extend throughthe length of the rounded ends 138 of the slit edges 134. While notillustrated, an end of the pins 144 may extend beyond the ends of theslit edges 134 wherein rotation of the pins 144 results in relativerotation of the knife edges 140. By way of example, the end of the pins144 may be configured as a gear with a corresponding actuator tofacilitate rotation of the pins 144.

FIGS. 24-28 illustrate another alternative technique for implementing acollimator assembly 12 having one or more adjustable slit apertures 108therein, in accordance with exemplary embodiments of the presenttechnique. Referring now to FIGS. 24 and 25, the collimator assembly 12may include a first set of panels 146 (e.g., panels 146 a-146 f) and asecond set of panels 148 (e.g., panels 148 a-148 f). While the first setof panels 146 and the second set of panels 148 are illustrated as eachincluding six panels, those of ordinary skill in the art will appreciatethat the present technique encompasses the use of more or less panels.As illustrated, the first set of panels 146 and the second set of panels148 may be arranged at least partially around the longitudinal axis 112of the collimator assembly 12 so that spaces between the first set ofpanels 146 and the second set of panels 148 define one or moreadjustable slit apertures 108 (e.g., adjustable slit apertures 108 a-108f) therein. As will be discussed in more detail below, the collimatorassembly 12 may be configured so that axial movement of at least one ofthe first set of panels 146 or the second set of panels 148 adjusts theaperture size of the adjustable slit apertures 108.

The first set of panels 146 and the second set of panels 148 may extendin a direction generally parallel to the longitudinal axis 112 of thecollimator assembly. Moreover, in exemplary embodiments, the first setof panels 146 and the second set of panels 148 may be arranged aroundthe longitudinal axis 112 in a generally polygonal configuration.Further, the first set of panels 146 and the second set of panels 148may be arranged in an alternating pattern so that each of the first setof panels 146 is adjacent to two of the second set of panels 148 andvice versa. By way of example, panel 146 a of the first set of panels148 is adjacent to panels 148 a and 148 b of the second set of panels148. In the illustrated embodiment, the first set of panels 146 arecoupled to a top ring 150 (e.g., a collar) at a first end 152 of thecollimator assembly 12, and the second set of panels 148 are coupled toa bottom ring 154 (e.g., a collar) at a second end 156 of the collimatorassembly 12, the second end 156 being opposite from the first end 152.

As previously mentioned, the first set of panels 146 and the second setof panels 148 may be arranged around the longitudinal axis 112 of thecollimator assembly 12 so that spaces between the first set of panels146 and the second set of panels 148 define one or more adjustable slitapertures 108 therein. For example, panel 146 a of the first set ofpanels 146 and panel 148 a of the second set of panels 148 may bearranged such that a space between the adjacent panels defines theadjustable slit aperture 108 a. In general, each of the panels in thefirst set of panels 146 and the second set of panels 148 has a slit edge158 (e.g., slit edges 158 a of panel 146 a) and opposing slit edges 160(e.g., opposing slit edge 160 a of panel 148 a). As illustrated, theslit edge 158 a of panel 146 a and the opposing slit edge 160 a of panel148 a are the portions of the respective panels that are adjacent to theadjustable slit aperture 108 a. As will be discussed in more detailbelow, the side of the slit edges 158 and the opposing slit edges 160may be angled with respect to the panel's axis.

In exemplary embodiments, axial movement of at least one of the firstset of panels 146 or the second set of panels 148 adjusts the aperturesize of the adjustable slit apertures 108. By way of example, thecollimator assembly 12 may be configured to allow top ring 150 andbottom ring 154 to move along the longitudinal axis 112 of thecollimator assembly 112. Accordingly, movement of at least one of thetop ring 150 or bottom ring 154 in a direction away from each otheralong the longitudinal axis 112 should enlarge the adjustable slitapertures 108. In a similar manner, movement of at least one of the topring 150 or the bottom ring 154 in a direction toward each other alongthe longitudinal axis 112 should reduce the size of the adjustable slitapertures 108. As illustrated by FIGS. 24 and 25, the adjustable slitapertures 108 should enlarge as the top ring 150 and bottom ring 154 aremoved away from each other along the longitudinal axis 112 of thecollimator assembly 12.

Referring now to FIG. 26, a top view of a collimator assembly 12 similarto the collimator assembly of FIGS. 24 and 25 is illustrated, inaccordance with embodiments of the present technique. As illustrated,the top ring 150 at the first end 152 of the collimator assembly 12 isremoved to illustrate the first set of panels 146 and the second set ofpanels 148. In the illustrated embodiment, each of the panels includes aslit edge and an interlocking side. For example, panel 146 a of thefirst set of panels 146 includes a slit edge 158 a and an interlockingside 162 a. As previously mentioned, the space between the slit edge 158a of panel 146 a of the first set of panels 146 and the opposing slitedge 160 a of panel 148 a of the second set of panels 148 defines anadjustable slit aperture 108 a. Furthermore, the opposite side (e.g.,interlocking side 162 a) of one of the first set of panels 146 may beinterlocked with an opposing side (e.g., opposing interlocking side 164b) one of the second set of panels 148. As illustrated, the interlockingside 162 a of panel 146 a may be interlocked with the opposinginterlocking side 164 b of panel 148 b. Moreover, to permit axialmovement of at least one of the first set of panels 146 or the secondset of panels 148, the panels may be slidably interlocked. Accordingly,at least one of the first set of panels 146 or the second set of panels148 may be moved along the longitudinal axis 112 of the collimatorassembly 12 for adjustment of the aperture size of the adjustable slitapertures 108.

While FIGS. 26 illustrates the slit edges 158 and the opposing slitedges 160 as having a knife-edge configuration, other aperture edgeconfigurations (e.g., rounded) may also be suitable. Those of ordinaryskill in the art will appreciate that the aperture edge configurationmay be selected based on, inter alia, the desired point-spread-functionresponse.

Referring now to FIG. 27, a perspective view of a collimator assembly 12similar to the collimator assemblies of FIGS. 24-26 is illustrated, inaccordance with embodiments of the present technique. In the illustratedembodiment, the first set of panels 146 have first alignment pins 166extending therefrom on the second end 156 of the collimator assembly 12,and the second set of panels 148 have second alignment pins 167extending therefrom on the first end 152 of the collimator assembly 12.As illustrated, the first alignment pins 166 may be coupled to the endof the first set of panels 146 that is opposite the end that is coupledto the top ring 150. Further, the second alignment pins 167 may becoupled to the end of the second set of panels 148 that is opposite theend that is coupled to the bottom ring 154. When the collimator assembly12 is assembled, the first alignment pins 166 on the second end 156 ofthe collimator assembly 12 may be disposed in corresponding first pinopenings 168 in the bottom ring 154. In a similar manner, the secondalignment pins 167 on the first end 152 of the collimator assembly 12may be disposed in corresponding second pin openings 171 in the top ring150. Among other things, the first and second alignment pins 166 and 167may facilitate relative alignment of the top ring 150 and bottom ring154 and alignment of the first and second set of panels 146 and 148.

As illustrated in FIG. 27, the collimator assembly 12 may furtherinclude rod assemblies 169. In general, the rod assemblies 169 may beused to axially position the top ring 150 and/or the bottom ring 154 soas to adjust the aperture size of the adjustable slit apertures 108. Inthe illustrated embodiment, the rod assemblies 169 include rods 170, topsprings 172, bottom springs 174, and gears 175. In exemplaryembodiments, each of the rods 170 include a threaded portion 176, a topcollar 178, a bottom collar 180, and a lower end 182. As illustrated thethreaded portion 176 is located on the opposite end of each of the rods170 from the lower end 182. The top collar 178 is located between thethreaded end 176 and the bottom collar 180. The bottom collar 180 islocated between the top collar 178 and the lower end 182.

In the illustrated embodiment, rod assemblies 169 are located on theperiphery of the collimator assembly 12 and are disposed generallyparallel to the longitudinal axis 112 of the collimator assembly 12. Thethreaded end 176 of each of the rods 170 may be threaded through acorresponding threaded rod opening 184 in the top ring 150. The topsprings 172 are disposed over the rods 170 between the threaded rodopening 184 and the top collar 178. In exemplary embodiments, the topsprings 172 may be pre-loaded to prevent backlash of the upper ring 150and, in turn, backlash of the second set of panels 148. The lower end182 of each of the rods 170 may be disposed in a corresponding rodopening 186 in the bottom ring 154. Lower springs 174 may be disposedover the lower end 182 of the rods 170 between the rod opening 186 andthe gears 175. The bottom ring 154 may be configured to allow forrotation of the rods 170. The rods 170 generally should not slidethrough the rod opening 186 when assembled as the rods 170 should beconstrained by lower collar 180 and bottom springs 174. In exemplaryembodiments, the bottom springs 174 may be pre-loaded to preventundesired movement of the bottom ring 154 and, in turn, undesired motionof the first set of panels 146.

As described above, the rod assemblies 169 may be used to axiallyposition the top ring 150 and/or the bottom ring 154 so as to adjust theaperture size of the adjustable slit apertures 108. In general, a commongear (not illustrated) may be used to drive the gears 175. Rotation ofthe gears 175 results in respective rotation of the rod assemblies 169,resulting in axial separation of the top ring 150 and the bottom ring154. In the illustrated embodiment, counter-clockwise rotation (asviewed from below) of the rod assemblies 169 should result in upwardmovement of the top ring 150 and, in turn, upward movement of the firstset of panels 146. As the first set of panels 146 are driven upward thesize of the adjustable slit apertures 108 should increase. In a similarmanner, clockwise rotation (as viewed from below) of the rod assemblies169 should result in downward movement of the top ring 150 and, in turn,downward movement of the first set of panels 146. As the first set ofpanels 146 are driven downward the size of the adjustable slit apertures108 should decrease. In this manner, the rod assemblies 169 may be usedto adjust the aperture size of the adjustable slit apertures 108. Aswill be appreciated, while the preceding description discussion ofclockwise and counter-clockwise assumes a right-hand thread on rod 170,the present technique also encompasses other thread configurations, suchas a left-hand thread.

The collimator assembly 12 illustrated by FIGS. 24-28 may be assembledvia any suitable technique. In accordance with one embodiment, the firstset of panels 146 and the second set of panels 148 may be coupled to thetop ring 150 and the bottom ring 154, respectively. Each of rods 170 maybe inserted through the corresponding rod openings 186 in the bottomring 154 until the bottom collar 180 of each of the rods 170 is adjacentto the bottom ring 154. By way of example, the rods 170 may be insertedthrough the rod openings 186 until the bottom collar 180 contacts a topsurface 188 of the bottom ring 154. The bottom springs 182 may be placedover the lower end 182 of each of the rods 170 that extends through therod openings 186 in the bottom ring 154. In one embodiment, the gears175 may be coupled to the end of each of the rods 170 below the bottomsprings 182. By way of example, the gears 175 may be slide fitted overthe ends of the rods 170. Moreover, a glue (such as a slow-curing glue)may be applied to an inner surface of the gears 175 to facilitatebonding to the rods 170. However, while glue may be used, in certainembodiments, it may be desirable for the gears 175 to rotate withrespect to the rods 170 until the desired phase angles of all gears 175and the common driving gear (not shown) are set after mounting of thetop ring 150, then glue may be applied. The top springs 172 may beplaced over the threaded ends 176 of the rods 170. The threaded ends 176of the rods 170 may be inserted the threaded rod openings 184 of the topring 150. By way of example, the threaded ends 176 may be threaded intothe threaded rod openings 184. While the threaded ends 176 are insertedthrough the threaded rod openings 184, the top ring 150 may be heldparallel to the bottom ring 154. By way of example, the top ring 150 maybe mounted in a position parallel to the bottom ring 154. An independentreference, such as two parallel plates, may be used to position the topring 150 and the bottom ring 154 parallel with respect to one another.The gears 175 may be rotated to engage a driving gear (not shown). Byway of example, the gears 175 may be rotated with respect to the rods170 to engage the driving gear. Where glue is used, the glue placed onthe inner surfaces of the gears 175 may set to lock the gears 175 andthe rods 170, after the gears 175 have been engaged with the drivinggear. Those of ordinary skill in the art will appreciate the presenttechnique encompasses alternative methods of assembling the collimatorassembly 12.

Referring now to FIG. 28, an exemplary panel 146 a of the first set ofpanels 146 is illustrated, in accordance with an embodiment of thepresent technique. As previously described, the panel 146 a includes aslit edge 158 a and an interlocking side 162 a. As illustrated, the slitedge 158 a is angled with respect to the axial direction 192 of thepanel 146 a. Those of ordinary skill in the art will appreciate thatthis slit angle 190 may be varied to impact the adjustment of theaperture size of the adjustable slit aperture 108 defined the slit edge158 a and a corresponding slit edge (e.g., opposing slit edge 160 a onFIG. 26) of one of the second set of panels 148. By way of example,reducing the slit angle 190 should increase the axial movement of thetop ring 150 and/or the bottom ring 154 needed to adjust the aperturesize. Similarly, increasing the slit angle 190 should decrease the axialmovement needed to adjust the aperture size. Those of ordinary skill inthe art should be able to select a suitable slit angle 190 based on anumber of factors, included the desired resolution and sensitivity for aparticular application. By way of example, a smaller slit angle 190 maybe desired in higher resolution applications, while an increased slitangle 190 may be desired in lower resolution, higher sensitivityapplications.

IV. Exemplary Combined Slit/Pinhole Aperture Collimator Embodiments

While specific reference is made in the present discussion to slitaperture collimators and pinhole aperture collimators, it should beappreciated that the present technique may be applicable to combinedslit/pinhole aperture collimators. Combined slit/pinhole aperturecollimators may be useful because the pinhole apertures may be focusedon a small field of view while the slit apertures may be focused on alarger field of view that may, for example, overlap with the small fieldof view. By focusing the slit and pinhole apertures on different fieldsof view, activity outside the small field of view should be properlyimaged and, thus, not be aliased into the small field of view duringreconstruction. Also, the slit and pinhole apertures may providecomplementary information about the distribution of aradiopharmaceutical tracer in various body tissues. By way of example,in a subject suspected of having cancer in a particular organ, thepinhole apertures could be focused on the target organ while the slitapertures could be focused on a large field of view in order to screenfor metastatic tumors. Furthermore, the slit and pinhole apertures mayhave different spatial resolutions and sensitivities. By way of example,the image reconstruction quality may be improved by properly accountingfor the combination of higher spatial resolution data over a small fieldof view and lower spatial resolution data over a larger field of view.

Referring now to FIG. 29, a combined collimator 194 is illustrated, inaccordance with exemplary embodiments of the present technique. In theillustrated embodiment, the combined collimator 194 includes a slitaperture portion 196 having one or more adjustable slit apertures 108therein and a pinhole aperture portion 198 having one or more adjustablepinhole apertures 40 therein. While not illustrated, the SPECT system 10could further include one or more septa spaced on a side of the slitaperture portion 196 opposite from the field of view that would, forexample, co-rotate with the combined collimator 194. At least one of theslit apertures 108 and/or at least one of the pinhole apertures 40 mayhave an aperture size that is adjustable. Any of the techniquesdescribed herein may be utilized for adjustment of the apertures size ofthe slit apertures and/or pinhole apertures with an adjustable aperturesize. Moreover, the aperture size may be configured for adjustmentduring an examination.

While the preceding discussion has described the combined collimator 194as having a single slit aperture portion 196 and a single pinholeaperture portion 198, one of ordinary skill in the art will recognizethat the design may be extended to include multiple intermingled slitand pinhole aperture portions. In exemplary embodiments, for each slitaperture portion, a corresponding set of spaced septa could be placedbetween the combined collimator 194 and the detector assembly to defineslit/septa gamma ray pathways. As will be appreciated, the combinedcollimator 194 may or may not rotate.

V. Exemplary Cross-Slit Aperture Collimator Embodiments

While specific reference in the preceding discussion is made to pinholeaperture collimators and slit aperture collimators with correspondingsepta, it should be appreciated that the present technique is applicableto cross-slit aperture collimators. Referring now to FIG. 30, anexploded view of a cross-slit aperture collimator 200 is illustrated,which may be configured in accordance with exemplary embodiments of thepresent technique. In the illustrated embodiment, cross-slit aperturecollimator 200 includes an inner slit aperture collimator 202 and anouter slit aperture collimator 204. As illustrated, the cross-slitaperture collimator 200 at least partially encloses the field of view26. While FIG. 30 is an exploded view, the cross-slit aperturecollimator 200 should be assembled so that the inner slit aperturecollimator 202 is disposed closer to the field of view 26 than the outerslit aperture collimator 204. As will be discussed in more detail below,the cross-slit aperture collimator 200 should be configured such thatthe inner slits 206 in the inner slit aperture collimator 202 and theouter slits 208 in the outer slit aperture collimator 204 define one ormore adjustable apertures through the cross-slit aperture collimator200. Aperture size of least one of the inner slits 206 or the outerslits 208 may be adjusted to adjust the aperture size of the one or moreadjustable apertures. Moreover, spacing between the inner surface(s) ofthe outer slit aperture collimator 204 and the outer surface(s) of theinner slit aperture collimator 202 may be chosen to position the outerslit aperture collimator 204 anywhere in the volume between the innerslit aperture collimator 202 and the detector assembly 14. By way ofexample, the outer slit aperture collimator 204 may be positioned closeto but not touching the inner slit aperture collimator 202.

Further, the inner and outer slit collimators 202 and 204 may bemechanically coupled or placed in contact with each other, so as torotate together, or they may be decoupled, so as to rotate separately asdesired to adjust the positions of the apertures.

The inner slit aperture collimator 202 includes a plurality of innerslits 206 therein. In the illustrated embodiment, these inner slits 206extend in a direction generally perpendicular to the longitudinal axis112 of the cross-slit aperture collimator 200. In addition, the innerslit aperture collimator 202 includes a plurality of sections spacedalong the longitudinal axis 112 such that spaces between the sectionsdefine the inner slits 206. By way of example, the spaced sections mayinclude a plurality of inner cylindrical sections 210 spaced along thelongitudinal axis 112 of the cross-slit aperture collimator 200 so as todefine the inner slits 206. In the illustrated embodiments, the innercylindrical sections 210 are coupled by rods 212 that extend in adirection parallel to the longitudinal axis 112. In exemplaryembodiments, the rods 212 may be coupled to exterior surfaces of each ofthe inner cylindrical sections 210 of the inner slit aperture collimator202. For further support, each end of the rods 212 may be coupled to acoupling mechanism, such as bands 214 or collars. By way of example,each of bands 214 may be coupled to the inner cylindrical sections 210located at each end of the inner slit aperture collimator 202. While theinner cylindrical sections 210 of the inner slit aperture collimator 202are illustrated as separate sections, the present technique encompassesthe use of a unitary inner slit collimator. That is, the inner slitaperture collimator 202 may be fabricated as a solid piece having one ormore slits therein. The inner slit aperture collimator 202 may also beconstructed as a unitary piece in which the slits are filled by amaterial that provides mechanical support but that also allows mostgamma rays to pass through the slit without interaction. Another exampleincludes rods inserted though small holes drilled along the wall ofcylindrical sections 210 (axial direction 112) and small spacers placedbetween cylindrical sections 210. The rods may run along the axialdirection 112, for example.

The outer slit aperture collimator 204 includes a plurality of outerslits 208 therein. In the illustrated embodiment, the outer slits 208extend in a direction generally parallel to the longitudinal axis 112 ofthe cross-slit aperture collimator 200. In addition, the outer slitaperture collimator 204 includes a plurality of sections spaced aroundthe longitudinal axis 112 of the cross-slit aperture collimator 200 suchthat spaces between the sections define the outer slits 208. By way ofexample, the spaced sections may be or include a plurality of outerpanels 216 spaced along and extending generally parallel to thelongitudinal axis 112 of the cross-slit aperture collimator 200 so as todefine the outer slits 208. For support, the outer panels 216 may becoupled by a coupling mechanism, such as bands 214 or collars. By way ofexample, each of the bands 214 may be coupled to each of the outerpanels 216 at the respective ends of the cross-slit aperture collimator200. While the outer panels 216 are illustrated in FIG. 30 as curvedsections, the present technique encompasses the use of sections that arenot curved. In addition, while the outer panels 216 are illustrated asseparate sections, the present technique encompasses the use of aunitary outer slit collimator. That is, the outer slit aperturecollimator 204 may be fabricated as a solid piece having one or moreslits therein. The outer slit aperture collimator 204 may also beconstructed as a unitary piece in which the slits are filled by amaterial that provides mechanical support but that also allows mostgamma rays to pass through the slit without interaction.

Referring now to FIG. 31, a portion of the detector assembly 14 and aportion of the cross-slit aperture collimator 200 are illustrated toillustrate the apertures defined by the alignment of the inner slits 206and the outer slits 208, in accordance with an embodiment of the presenttechnique. As previously mentioned, the cross-slit aperture collimator200 should be configured such that the inner slits 206 and the outerslits 208 define one or more adjustable apertures 218. Gamma rays 30that do not pass through the one or more adjustable apertures 218 shouldbe absorbed by the cross-slit aperture collimator 200. In theillustrated embodiment, the adjustable apertures are defined by theintersection of the inner slits 206 and the outer slits 208. Theadjustable apertures 218 allow gamma rays 30 emanating from the field ofview 26 to pass through the cross-slit aperture collimator 200 to impactthe detector array 14.

Those of ordinary skill in the art will appreciate that the resolutionof the SPECT system 10 is based in part on the aperture size of the oneor more adjustable apertures 218. As previously mentioned, theadjustable apertures 218 have an aperture size that is adjustable. Asthe adjustable apertures 218 are defined by the intersection of theinner slits 206 and the outer slits 208, the size of the adjustableapertures 218 is based on the width of the inner slits 206 and the outerslits 208. In general, adjustment of the width of at least one of theinner slits 206 or the outer slits 208 should result in a correspondingaperture size adjustment for the adjustable apertures 218. In general,the inner slits 206 and/or the outer slits 208 may have the same ordifferent widths. By way of example, the inner slits 206 and the outerslits 208 may have two or more different widths. In exemplaryembodiments, each of the inner slits 206 and/or each of the outer slits208 may have, or be adjusted, to a width in the range of from about 0.1mm to about 10 mm, typically in the range of from about 1 mm to about 5mm. Those of ordinary skill in the art will appreciate that the choiceof slit widths depends upon the system geometry (e.g., detector array 14location and subject field of view 26) and intended imagingapplications. Adjustment of the adjustable apertures 218 to differentsizes may provide different resolving power. By differing the aperturesize, the spatial resolution and sensitivities of the SPECT system 10may be changed. The image reconstruction algorithm should appropriatelymodel the system response of the various apertures.

Moreover, in the illustrated embodiment, the inner slits 206 aregenerally orthogonal to the outer slits 208 (e.g., the angle of theintersection between the inner slits 206 and the outer slits 208 isapproximately 90°). Because the slits are arranged in the orthogonalconfiguration, the adjustable apertures 218 defined by the cross-slitaperture collimator 200 forms a four-sided hole therethrough. Asillustrated, the inner slits 206 and the outer slits 208 generally havethe same width so that the adjustable apertures 218 defined by theintersection of the slits have a generally square shape. Exemplaryembodiments of the present technique also may be provided with the innerslits 206 and the outer slits 208 having different widths so that theadjustable apertures 218 defined by the slits would have a generallyrectangular shape. Moreover, exemplary embodiments of the presenttechnique also may be provided with the inner slits 206 generallyoblique to the outer slits 208 (e.g., the angle of the intersectionbetween the inner slits 206 and the outer slits 208 is different from90°), so that the adjustable apertures 218 defined by the intersectionof the slits would have a generally rhombus or parallelogram shape. Inaddition, those of ordinary skill in the art will also appreciate thatthe spacing between the slits in the inner and outer slit aperturecollimators 202 and 204 may or may not be constant throughout thecross-slit aperture collimator 200.

While the preceding discussion of FIGS. 30 and 31 has described theinner slit aperture collimator 202 as having inner slits 206 extendinggenerally perpendicular to the longitudinal axis 112 of the cross-slitaperture collimator 200 and the outer slit aperture collimator 204 ashaving outer slits 208 extending in a direction generally parallel tothe longitudinal axis 112, one of ordinary skill in the art willrecognize that the present technique may be implemented with collimatorassemblies having inner and outer slit aperture collimators 202 and 204having alternative slit configurations. For example, the inner slits 206may extend in a direction generally parallel to the longitudinal axis112 of the cross-slit aperture collimator 200 while the outer slits 208in outer slit aperture collimator 204 may extend in a directiongenerally perpendicular to the longitudinal axis 112 of the cross-slitaperture collimator 200. In another embodiment, the inner slits 206and/or the outer slits 208 may extend in a direction generally diagonalto the longitudinal axis 112 of the cross-slit aperture collimator 200.

VI. Exemplary Combination SPECT/CT Embodiments

While specific reference in the present discussion is made to a SPECTsystem, it should be appreciated that the present technique is notintended to be limited to this or any other specific type of imagingsystem or modality. Rather, exemplary embodiments of the presenttechnique may be used in conjunction with other imaging modalities,e.g., coded-aperture astronomy. In addition, SPECT system 10 may becombined with a second imaging system, such as a CT system or a magneticresonance imaging (MRI) system. By way of example, the SPECT system 10may be combined in the same gantry with a CT system. As illustrated inFIG. 32, a SPECT/CT imaging system includes SPECT system 10 and CTsystem 220. By way of example, the SPECT system 10 and the CT system 220are shown as separate modules, aligned along a common longitudinal axis,and sharing a single subject support 24. As illustrated in FIG. 33, CTsystem 220 includes a source 222 of X-ray radiation configured to emit astream of radiation 224 in the direction of the field of view 26 and anX-ray detector assembly 226 configured to generate one or more signalsin response to the stream of radiation. Those of ordinary skill in theart will appreciate that in the third-generation CT configurationillustrated in FIG. 33, the source 222 and the X-ray detector assembly226 generally rotate in synchrony around the field of view 26 whileacquiring a plurality of lines of response passing through the subject,so that an X-ray tomographic attenuation image may be reconstructed.Other CT configurations may be employed, including the shared use of atleast a portion of the SPECT detector assembly 14 as the X-ray detectorassembly 226. Further, the SPECT and CT images may be acquiredsequentially, in any order, by repositioning the subject, orconcurrently by sharing the detector array. The images generated withthe CT system 220 may then be used to generate gamma ray attenuationmaps, for example, to calculate attenuation and/or scatter correctionduring the SPECT image reconstruction. In addition, the CT anatomicalimages may be combined with the SPECT functional images.

While the collimator assembly 12 is illustrated on the preceding figuresas being generally cylindrically shaped, the present techniqueencompasses the employment of collimator assemblies that are notgenerally cylindrically shaped. By way of example, the collimatorassembly 12 may be or include a flat panel having one or more adjustableapertures (e.g., adjustable pinhole apertures 40 or adjustable slitapertures 108) therein. Furthermore, one of ordinary skill in the artwill recognize that the collimator assembly 12 and detector assembly 14may be combined in modules and positioned to view portions of the fieldof view. If only a few collimator/detector modules are deployed, thenthey may be moved to a plurality of positions during image acquisitionin order to acquire sufficient data for tomographic imagereconstruction. Alternatively, if sufficient collimator/detector modulesare deployed, then they may remain stationary during image acquisitionand yet acquire sufficient data for tomographic image reconstruction.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A collimator assembly comprising a plurality of apertures therein,wherein the apertures have respective aperture sizes that are configuredfor adjustment while data collection is occurring, and wherein thecollimator assembly is configured so that gamma rays can pass throughthe apertures, but the remainder of the collimator assembly issubstantially gamma ray absorbent.
 2. The collimator assembly of claim1, wherein the apertures comprise one or more pinhole apertures.
 3. Thecollimator assembly of claim 1, wherein the apertures comprise slitapertures.
 4. The collimator assembly of claim 3, wherein the collimatorassembly is configured so that the slit apertures have a first aperturesize at a first diameter of the collimator assembly, and wherein theslit apertures have a second aperture size at a second diameter of thecollimator assembly.
 5. The collimator assembly of claim 3, wherein thecollimator assembly is configured so that dilation of the collimatorassembly increases an aperture size of the slit apertures.
 6. Thecollimator assembly of claim 3, wherein the collimator assemblycomprises an inner collimator and an outer collimator arranged to definethe slit apertures, wherein the collimator assembly is configured sothat rotation of at least one of the inner collimator or the outercollimator adjusts an aperture size of each of the slit apertures. 7.The collimator assembly of claim 6: wherein the inner collimatorcomprises panels spaced at least partially around a longitudinal axis ofthe collimator assembly and disposed in a direction generally parallelto the longitudinal axis; and wherein the outer collimator comprisespanels spaced at least partially around a longitudinal axis of thecollimator assembly and disposed in a direction generally parallel tothe longitudinal axis.
 8. The collimator assembly of claim 7, whereineach of of the panels of the inner collimator comprises a first portionthat overlaps with one of the panels of the outer collimator and asecond portion, wherein a space between the second portion and anotherone of the panels of the outer collimator defines one of the slitapertures.
 9. The collimator assembly of claim 3, wherein the collimatorassembly comprises a first panel and a second panel arranged so that aspace between an edge of the first panel and an edge of the second paneldefines one of the slit apertures, wherein the collimator is configuredso that rotation first of at least one of the edge of the first panel orthe edge of the second panel adjusts an aperture size of the respectiveslit aperture.
 10. The collimator assembly of claim 9, wherein the firstpanel comprises a panel body having a rounded recess configured toaccept a rounded end of the edge of the first panel.
 11. The collimatorassembly of claim 3, wherein the collimator assembly comprises a firstset of panels and a second set of panels arranged to define the slitapertures, wherein the collimator assembly is configured so that axialmovement of at least one of the first set of panels or the second set ofpanels adjusts an aperture size of the slit apertures.
 12. Thecollimator assembly of claim 11: wherein the first set of panels arearranged at least partially around a longitudinal axis of the collimatorassembly and disposed in a direction generally parallel to thelongitudinal axis; wherein the second set of panels arranged at leastpartially around the longitudinal axis and disposed in a directiongenerally parallel to the longitudinal axis, wherein the first set ofpanels and the second set of panels are arranged around the longitudinalaxis in an alternating pattern; and wherein each of the slit aperturesis defined by a space between an edge of one of the first set of panelsand an opposing edge of one of the second set of panels.
 13. Thecollimator assembly of claim 1, wherein the apertures comprise one ormore pinhole apertures and one or more slit apertures.
 14. Thecollimator assembly of claim 1, wherein the collimator assemblycomprises an inner collimator comprising inner slit apertures thereinand an outer collimator comprising outer slit apertures therein, whereinthe apertures in the collimator assembly are defined by intersection ofthe inner slit apertures and the outer slit apertures.
 15. An imagingsystem comprising: a collimator assembly comprising a plurality ofapertures therein, wherein the apertures have respective aperture sizesthat are configured for adjustment during an examination; and a detectorassembly configured to generate one or more signals in response to gammarays that pass through the apertures of the collimator assembly.
 16. Theimaging system of claim 15, wherein the imaging system comprises asingle photon emission computed tomography system or a combined singlephoton emission computed tomography system/x-ray computed tomographysystem.
 17. The imaging system of claim 15, wherein the detectorassembly comprises at least one of an array of solid-state detectorelements or a scintillator assembly coupled to light sensors.
 18. Theimaging system of claim 15, comprising: a module configured to receivethe one or more signals and to process the one or more signals togenerate one or more images; and an image display workstation configuredto display the one or more images.
 19. The imaging system of claim 15,wherein the aperture sizes are configured for adjustment without removalof a subject from a field of view of the imaging system.
 20. The imagingsystem of claim 15, wherein the collimator assembly is configured sothat the apertures have a first aperture size at a first diameter of thecollimator assembly, and wherein the apertures have a second aperturesize at a second diameter of the collimator assembly.
 21. The imagingsystem of claim 15, wherein the collimator assembly comprises an innercollimator and an outer collimator arranged to define slit apertures,wherein the collimator assembly is configured so that rotation of atleast one of the inner collimator or the outer collimator adjusts anaperture size of each of the slit apertures, wherein the apertures inthe collimator assembly comprise slit apertures.
 22. The imaging systemof claim 15, wherein the collimator assembly comprises a first panel anda second panel arranged so that a space between an edge of the firstpanel and an edge of the second panel defines one of the slit apertures,wherein the collimator is configured so that rotation of at least one ofthe edge of the first panel or the edge of the second panel adjusts anaperture size of each of the slit apertures, wherein the apertures inthe collimator assembly comprise slit apertures.
 23. The imaging systemof claim 15, wherein the collimator assembly comprises a first set ofpanels and a second set of panels arranged to define slit apertures,wherein the collimator assembly is configured so that axial movement ofat least one of the first set of panels or the second of panels adjustsan aperture size of each of the slit apertures.
 24. A method of imaginga volume comprising: positioning at least a portion of a subject in afield of view of an imaging system, wherein the imaging system comprisesa collimator assembly and a detector assembly; and adjusting an aperturesize of a plurality of apertures in the collimator assembly while theportion of the subject is positioned in the field of view; collimatinggamma rays emitted from the subject using the collimator assembly; anddetecting the collimated gamma rays.
 25. The method of claim 24, whereinadjusting the aperture size comprises adjusting the diameter of thecollimator assembly from a first diameter to a second diameter.
 26. Themethod of claim 24, wherein adjusting the aperture size comprisesrotating an edge of a first panel to adjust a size of a space betweenthe first panel and a second panel, wherein the space between the firstpanel and the second panel defines one of the apertures.
 27. The methodof claim 24, wherein the collimator assembly comprises an innercollimator and an outer collimator arranged to define slit apertures,wherein the adjusting the aperture size comprises rotating at least oneof the inner collimator or the outer collimator.
 28. The method of claim24, wherein adjusting the aperture size comprises axially moving atleast one of a first set of panels or a second set of panels, whereinthe first set of panels and the second panels are arranged at leastpartially around a longitudinal axis of the collimator assembly so thatspaces between the first set of panels and the second set of panelsdefines the apertures in the collimator assembly.
 29. A method ofimaging a volume comprising: positioning at least a portion of a subjectin a field of view of an imaging system, wherein the imaging systemcomprises a collimator assembly and a detector assembly; and collimatinggamma rays emitted from the subject using the collimator assembly;detecting the collimated gamma rays; automatically adjusting an aperturesize of a plurality of apertures in the collimator assembly to increaseresolution of the imaging system; collimating gamma rays emitted fromthe subject using the adjusted collimator assembly; and detecting thecollimated gamma rays.